method for determining the presence, absence or characteristics of an analyte, method and apparatus

专利摘要:
METHOD FOR DETERMINING THE PRESENCE, ABSENCE OR CHARACTERISTICS OF AN ANALYST, METHOD AND APPARATUS FOR SEQUENCING AN ANALYTIS WHICH IS A TARGET POLYNUCLEOTIDE, AND, KITThe invention relates to a new method of determining the presence, absence or characteristics of an analyte. The analyte is attached to a membrane. The invention also relates to the sequencing of nucleic acid.
公开号:BR112013030529A2
申请号:R112013030529-0
申请日:2012-05-25
公开日:2020-08-04
发明作者:James Clarke；James White；John Milton；Clive Brown
申请人:Oxford Nanopore Technologies Limited；
IPC主号:

专利说明:

1/106 “METHOD FOR DETERMINING THE PRESENCE, ABSENCE OR CHARACTERISTICS OF AN ANALYTICAL, METHOD AND APPLIANCE
FOR SEQUENCING AN ANALYTIS WHICH IS A TARGET POLYNUCLEOTIDE, KIT ”Field of the invention The invention relates to a new method of determining the presence, absence or characteristics of an analyte. The analyte is attached to a membrane. The invention also relates to the sequencing of nucleic acid. Background to the invention There is currently a need for fast and inexpensive nucleic acid sequencing technologies (e.g., DNA or RNA) across a wide range of applications. Existing technologies are slow and expensive mainly because they rely on amplification techniques to produce large volumes of nucleic acid and require a high amount of special fluorescent chemicals for signal detection. Nanopores have enormous potential as direct, electrical biosensors for polymers and a variety of small molecules. In particular, recent focus has been given to nanopores as a potential DNA sequencing technology. Two methods for DNA sequencing have been proposed; 'Exonuclease sequencing', where the bases are processively cleaved from the polynucleotide by an exonuclease and are then individually identified by the nanopore and also 'Filament sequencing', where a single strand of DNA is passed through the pore and the nucleotides are directly identified. Filament Sequencing may involve the use of a DNA treatment enzyme to control the movement of the polynucleotide through the nanopore.
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When a potential is applied through a nanopore, there is a drop in current flow when an analyte, such as a nucleotide, transiently resides in the tube for a certain period of time.
The nanopore detection of the analyte gives a known current signature and duration block. the concentration of an analyte can then be determined by the number of blocking events per unit time for a single pore.
For nanopore applications, such as DNA sequencing, efficient analyte capture from the solution is required.
For example, in order to give the DNA treatment enzyme used in DNA sequencing a duty cycle high enough to obtain efficient sequencing, the number of interactions between enzyme and polynucleotide needs to be maximum, so that a new polynucleotide is bound as soon as the current one is finished.
Therefore, in DNA sequencing, it is preferred to have the polynucleotide in as high a concentration as possible so that, as soon as one enzyme finishes its processing, the next one is readily available for binding.
This becomes a particular problem as the concentration of polynucleotide, such as DNA, becomes limiting, for example, the DNA of cancer cell samples for epigenetics.
The more diluted the sample the more time between sequencing runs, to the point where the binding of the first polynucleotide is so limiting that it is impractical.
The limits of nanopore detection have been estimated for several analytes.
The capture of a synthetic piece of 92 nucleotides of single-stranded DNA (ssDNA) by a protein nanopore (hemolysin) was determined to be at a frequency of 3.0 ± 0.2 s-1 μM-1 (Maglia, Restrepo et 2008, Proc Natl Acad Sci USA 105 (50): 19720-5). The capture can be increased ~ 10 times by adding a ring of positive charges at the entrance to the hemolysin tube (23.0 ± 2 s-1 μM-1). To put this in context, 1
3/106 μM of 92 nucleotide ssDNA is equivalent to 31 μg of DNA required per single channel record, assuming a 1 ml cis chamber volume.
The genomic DNA purification kit that dominates the market from human blood (Qiagen's PAXgene Blood DNA Kit) currently gives expected yields between 150 and 500 μg of genomics from 8.5 ml of human whole blood.
Therefore, this reported increase in analyte detection is still well outside the step change required for ultra-sensitive detection and release.
Summary of the invention Surprisingly, ultra low concentration analyte release has been demonstrated by binding the analyte to a membrane in which the relevant detector is present.
This decreases the amount of analyte required in order to be detected by several orders of magnitude.
The degree to which the amount of analyte needed is reduced may not have been predicted.
In particular, surprisingly, an increase in the capture of single-stranded DNA by ~ 4 orders of magnitude from that previously reported has been reported.
Since both the detector and the analyte are now on the same plane, then ~ 103 M s-1 more interactions occur per second, since the diffusion of both molecules is in two dimensions instead of three dimensions.
This has dramatic implications for sample preparation requirements that are of key interest for diagnostic devices such as next generation sequencing systems.
In addition, attaching the analyte to a membrane has additional advantages for various nanopore-enzyme sequencing applications.
In Exonuclease Sequencing, when the DNA analyte is introduced, the pore can become blocked permanently or temporarily, preventing the detection of individual nucleotides.
When one end of the DNA analyte is located outside the pore, for example by binding or tied to the membrane, it was surprisingly found that this temporary block
4/106 or permanent is no longer observed.
By occupying one end of the DNA by binding it to the membrane it also acts to effectively increase the concentration of analyte in the detector and thus increasing the duty cycle of the sequencing systems.
This is discussed in more detail below.
Accordingly, the invention provides a method for determining the presence, absence or characteristics of an analyte, which comprises (a) attaching the analyte to a membrane and (b) letting the analyte interact with a detector present in the membrane and thereby determining the presence , absence or characteristics of the analyte.
The invention also provides: - a method of sequencing an analyte that is a target polynucleotide, comprising: (a) attaching the target polynucleotide to a membrane; (b) letting the target polynucleotide interact with a detector present in the membrane, wherein the detector comprises a transmembrane pore and an exonuclease, so that the exonuclease digests an individual nucleotide at one end of the target polynucleotide; (c) letting the nucleotide interact with the pore; (d) measuring the current that passes through the pore during the interaction and thereby determining the identity of the nucleotide; and (e) repeating steps (b) to (d) at the same end of the target polynucleotide and thereby determining the sequence of the target polynucleotide; - a method of sequencing an analyte that is a target polynucleotide, comprising: (a) attaching the target polynucleotide to a membrane; (b) letting the target polynucleotide interact with a detector present
5/106 in the membrane, wherein the detector comprises a transmembrane pore, so that the target polynucleotide moves through the pore; and (c) measuring the current passing through the pore as the target polynucleotide moves with respect to the pore and thereby determining the sequence of the target polynucleotide; - a kit for sequencing an analyte that is a target polynucleotide comprising (a) a transmembrane pore, (b) a protein that binds polynucleotide and (c) means for attaching the target polynucleotide to a membrane; and - an apparatus for sequencing an analyte that is a target polynucleotide, comprising (a) a membrane, (b) a plurality of transmembrane pores in the membrane, (c) a plurality of proteins that bind polynucleotide and (d) a plurality of membrane-bound target polynucleotides.
Description of the Figures Fig. 1 shows the absorption by the nanopore of an analyte.
A) Shows a nanopore with the current flow direction indicated by the gray arrows.
A predicted current trace is shown below.
B) Shows a nanopore with an analyte that translocates through the pore.
The direction of movement of the analyte is indicated by arrow 1 and the direction of current flow by the gray arrows.
A predicted current trace is shown below that shows how the current changes as the analyte travels through the pore.
Fig. 2 shows a method for tying nanopore DNA interactions.
Sections A and B show transiently tied ssDNA and how the current trace changes as the ssDNA travels through the pore.
Sections C and D show ssDNA stably tied and how the current trace changes as the ssDNA is captured by the pore.
Fig. 3 shows the capture of a DNA enzyme complex,
6/106 followed by the dissociation of DNA and enzyme, and the subsequent DNA deibridization. Fig. 4 shows the experimental configuration for the Example
2. The comparison between (1) a starter / standard DNA analyte in solution (A - top) where the material concentrations are in the high nanomolar range (400 nM of DNA used and 800 nN of enzyme used) and (2) a tied system (B - bottom) where the amount of material is subnanomolar (1 nM of DNA used and 5 nN of enzyme used). Fig. 5 shows the binding times of KF at the top of the nanopore for the unbound analyte (DNA) in the absence of KF (DNA concentration = 400 nM). Fig. 6 shows the KF binding times at the top of the nanopore for the untied analyte (DNA) in the presence of KF (DNA concentration = 400 nM, KF concentration = 800 nM). The KF binding was from 1 to 100 ms. Fig. 7 shows the KF binding times at the top of the nanopore for the analyte (DNA) tied in the absence of KF (DNA concentration = 1 nM). Fig. 8 shows the KF binding times at the top of the nanopore for the analyte (DNA) tied in the presence of KF (DNA concentration = 1 nM, KF concentration = 5 nM). KF binding was 0.1 to 10 s. Fig. 9 shows an example of a transiently tied up Phi29 DNA polymerase dsDNA polymerization decompression event. The drop in the current from the open pore level is considered to be a blockage caused by the capture of a complex of DNA: protein. This captured complex resides in the nanopore for ~ 5 seconds, giving a constant current level before rapidly changing between levels and then finally returning to the open pore level. This is considered to be a pause before unpacking starts and a single A moves through the tip
7/106 reader thus giving the current oscillation.
When the duplex has been fully decompressed, the target filament moves, the initiator and the polymerase dissociate and thus the current returns to the open pore level.
Fig. 10 shows an example of a decompression event mediated by the Phi29 DNA polymerase dsDNA in solution.
The drop in the current from the open pore level is considered to be a blockage caused by the capture of a complex of DNA: protein.
This captured complex resides in the nanopore for ~ 12 seconds, giving a constant current level before rapidly changing between levels and then finally returning to the open pore level.
This is considered to be a pause before the decompression is started and as the single A moves through the reading tip thus giving the current oscillation.
When the duplex has been fully decompressed, the target filament moves, the initiator and the polymerase dissociate and thus the current returns to the open pore level.
Fig. 11 shows an example of an unpackaged round event sequences for untied dsDNA analyte.
The number of levels observed as well as the level and duration for these are largely compatible with the tied experiments.
Fig. 12 shows an example of an unpacked round event sequences for tied dsDNA analyte.
The number of levels observed as well as the level and duration for these are broadly compatible with experiments with DNA in solution (not tied). Fig. 13 shows a plasmid map of stranded analytes from the Genomic DNA Filament Sequencing.
The primers were designated complementary to the PhiX 174 genomic DNA. The same sense primer was used for everyone and contained a 5'-50poliT region followed by 4 abasic sites before the complementary region.
The hybridization sites for the antisense primers were varied according to the size of
8/106 desired fragment.
Each antisense primer contained a 5'-cholesterol group.
Fig. 14 shows the PCR generation of stranded analytes from the Genomic DNA Filament Sequencing.
The primers were designed to complement the PhiX 174 genomic DNA. The same sense primer was used for everyone and contained a 5'-50poliT region followed by the 4 abasic sites before the complementary region.
The hybridization sites for the antisense primers were varied according to the desired fragment size.
Each antisense primer contained a 5'-cholesterol group.
To confirm the presence of the 50poliT region in 5 'of the sense filament, fragments were digested with the single-filament specific RecJ exonuclease 5'-3' (NEB) and this was analyzed on a gel.
Row 1 contains 50 nt ssDNA, 235 base pair dsDNA only.
Lane 2 contains 50 nt ssDNA, 235 base pair dsDNA that has been digested with the specific single-stranded 5'-3 'RecJ exonuclease (NEB). Row 3 contains 50nt ssDNA, 400 base pair dsDNA only.
Lane 4 contains 50 nt ssDNA, 400 base pair dsDNA that has been digested with the specific single-stranded 5'-3 'RecJ exonuclease (NEB). Row 5 contains 50 nt ssDNA, 835 base pair dsDNA only.
Lane 6 contains 50 nt ssDNA, 835 base pair dsDNA that has been digested with the specific single stranded 5'-3 'RecJ exonuclease (NEB). Fig. 15 shows decompression events for the 800 base pair amplified PhiX 174 fragment.
This 800 base pair sequence corresponds to the sequence between points 1 and 3 on the plasmid map shown.
Fig. 16 shows decompression events of the amplified PhiX 174 fragment of 200 base pairs.
This 200 base pair sequence corresponds to the sequence between points 1 and 2 on the plasmid map shown.
The 200mer sequence is aligned against the 800mer sequence
9/106 shown in Fig. 15 with conductive interval and zero track penalties (ie, it is free to start anywhere, but “internal” intervals are penalized). As expected, the 200mer sections line up with the front of the 800mer.
Fig. 17 shows schemes that tie analyte to nanopores in the solid state.
A) Shows mooring on a modified surface (mooring on a layer). B) Shows mooring to a modified surface (interaction with the surface). C) Shows mooring to a lipid monolayer on a modified surface.
D) Shows lashing to a lipid bilayer on a modified surface.
Fig. 18 shows methods for attaching double-stranded polynucleotides to a lipid membrane.
A) Shows a single tied dsDNA binding protein that interacts with dsDNA analyte.
B) Shows multiple stranded dsDNA binding proteins that interact with a single dsDNA analyte.
C) Shows a single bonded chemical group that interacts with dsDNA analyte.
Fig. 19 shows methods for attaching single-stranded polynucleotide analytes to lipid membranes.
A) Shows a single bound ssDNA binding protein that interacts with ssDNA.
B) Shows multiple stranded ssDNA binding proteins that interact with a single ssDNA.
C) Shows a single bonded chemical group that interacts with ssDNA.
Fig. 20 shows a schematic of a way to use a protein that binds polynucleotide to control the movement of DNA through a nanopore that uses a dsDNA binding protein to bind DNA to the membrane.
A) A DNA analyte (consisting of a ssDNA leader (gray region) linked to a dsDNA region) is attached to the membrane using a tied dsDNA binding protein, which results in an enhanced concentration on the membrane surface.
A protein that binds
10/106 polynucleotide capable of controlling the movement of polynucleotide is added to the cis compartment where it binds to the projection of 4 base pairs.
B) Under an applied voltage, the DNA analyte is captured by the nanopore via section 5 'leader (gray region) in the DNA.
C) Under the force of the applied field, DNA is pulled into the pore until the bound polynucleotide binding protein contacts the top of the pore and prevents further uncontrolled displacement.
In this process the antisense strand is removed from the DNA strand, therefore resulting in the dsDNA binding protein detaching from the strand.
D) In the presence of appropriate cofactors, the polynucleotide binding protein at the top of the pore moves along the DNA and controls the displacement of the DNA through the pore.
The movement of the polynucleotide binding protein, along the DNA in a 3 'to 5' direction, pulls the stranded DNA out of the pore against the applied field back into the cis compartment.
The last section of DNA to pass through the nanopore is the 5’-leader.
The arrow indicates the direction of movement of the DNA.
Fig. 21 shows a schematic of how to use a protein that binds polynucleotide to control DNA movement through a nanopore using a hybridized tie.
A) A DNA analyte (consisting of a ssDNA leader (gray region) attached to a dsDNA region) is attached to the membrane using a hybridized string, resulting in an enhanced concentration on the membrane surface.
A polynucleotide-binding protein capable of controlling the movement of DNA is added to the cis compartment where it binds to the projection of 4 base pairs.
B) Under an applied voltage, the DNA analyte is captured by the nanopore via the leading 5 'section (gray region) in the DNA.
C) Under the force of the applied field, DNA is pulled into the pore until the bound polynucleotide binding protein contacts the top of the pore and prevents further uncontrolled displacement.
In this process the polynucleotide that is
11/106 tied to the membrane (dotted line) is removed to be sequenced (black filament with gray leading region). D) In the presence of appropriate cofactors, the polynucleotide binding protein at the top of the pore moves along the DNA and controls the displacement of the DNA through the pore.
The movement of the polynucleotide binding protein, along the DNA in a 3 'to 5' direction, pulls the stranded DNA out of the pore against the applied field back into the cis compartment.
The last section of DNA to pass through the nanopore is the 5’-leader.
The arrow indicates the direction of DNA movement.
Fig. 22 shows a schematic of a way to use a protein that binds polynucleotide to control the movement of DNA through a nanopore using a hybridized tie.
A) A DNA analyte (consisting of ssDNA (black line with the leader sequence shown in gray) hybridized to a ssDNA tie (dashed line)) is attached to the membrane using a hybridized tie, which results in an enhanced concentration in the membrane surface.
A protein that binds polynucleotide capable of controlling the movement of DNA is added to the cis compartment where it binds to the projection of 4 base pairs.
B) Under an applied voltage, the DNA analyte is captured by the nanopore via the leading 5 'section (gray region) in the DNA.
C) Under the force of the applied field, DNA is pulled into the pore until the bound polynucleotide binding protein contacts the top of the pore and prevents further uncontrolled displacement.
In this process the filament that is tied to the membrane (dashed line) is removed from the ssDNA filament to be sequenced (black filament with gray leading region). D) In the presence of appropriate cofactors, the polynucleotide binding protein at the top of the pore moves along the DNA and controls the displacement of the DNA through the pore.
The movement of the polynucleotide binding protein, along the DNA in a 3 ’to 5’ direction, pulls the stranded DNA out of the pore
12/106 against the field applied back to the cis compartment.
The last section of DNA to pass through the nanopore is the 5’-leader.
The arrow indicates the direction of movement of the DNA.
Fig. 23 shows several methods of mooring a probe, which can be used for the detection of microRNA, on a membrane.
A) The probe can be permanently attached to the membrane.
In this case the probe region that hybridizes to the microRNA is in the center of the probe.
The barcode region (dotted region) of the probe, which is used to identify the probe, is located at the opposite end of the filament in relation to the mooring.
Bi and ii) The probe can be transiently tied to the membrane by internal hybridization.
In this example, the probe region that hybridizes to the microRNA is attached to one end of the filament.
The region with the barcode (dotted region), which is used to identify the probe, is located directly above the mooring and below the microRNA hybridization region.
In Bii) the hybridization region of the mooring to the probe is inverted in its direction of connection compared to Bi). Ci and ii) The probe can be transiently attached to the membrane by hybridization to one end of the probe.
In this example, the probe region that hybridizes to the microRNA is located in the center of the filament.
The barcode region (dotted region), which is used to detect the presence or absence of the microRNA, is located below the microRNA hybridization region on the opposite side of the probe in relation to the mooring.
In Cii) the hybridization region of the mooring to the probe is inverted in its direction of connection compared to Ci). Description of the Sequence Listing SEQ ID NO: 1 shows the optimized polynucleotide sequence in the codon encoding the MspA monomer of the NNN-RRK mutant.
SEQ ID NO: 2 (also referred to as “B1”) shows the amino acid sequence of the mature form of the NNN-RRK mutant from
13/106 MspA monomer.
The mutant lacks the signal sequence and includes the following mutations: D90N, D91N, D93N, D118R, D134R and E139K.
These mutations allow the DNA to transition through the MspA pore.
SEQ ID NO: 3 shows the polynucleotide sequence that encodes an α-hemolysin-M111R (α-HL-R) subunit. SEQ ID NO: 4 shows the amino acid sequence of an α-HL-R subunit.
SEQ ID NO: 5 shows the optimized polynucleotide sequence in the codon encoding Phi29 DNA polymerase.
SEQ ID NO: 6 shows the amino acid sequence of Phi29 DNA polymerase.
SEQ ID NO: 7 shows the codon-optimized polynucleotide sequence derived from the E. coli sbcB gene.
It encodes the E. coli exonuclease I enzyme (EcoExo I).
SEQ ID NO: 8 shows the amino acid sequence of the E. coli exonuclease I (EcoExo I) enzyme.
SEQ ID NO: 9 shows the codon-optimized polynucleotide sequence derived from the E. coli xthA gene.
It encodes the E. coli exonuclease III enzyme.
SEQ ID NO: 10 shows the amino acid sequence of the E. coli exonuclease III enzyme.
This enzyme performs distributive digestion of the 5 'nucleoside monophosphate of a double-stranded DNA strand (dsDNA) in a 3' to 5 'direction. The start of the enzyme in a filament requires a 5 'projection of approximately 4 nucleotides.
SEQ ID NO: 11 shows the codon-optimized polynucleotide sequence derived from the T. thermophilus recJ gene.
It encodes the T. thermophilus RecJ enzyme (TthRecJ-cd). SEQ ID NO: 12 shows the amino acid sequence of the T. thermophilus RecJ enzyme (TthRecJ-cd). This enzyme performs digestion
14/106 processive 5 'monophosphate nucleosides of ssDNA in a 5' to 3 'direction. The start of the enzyme in a filament requires at least 4 nucleotides.
SEQ ID NO: 13 shows the codon-optimized polynucleotide sequence derived from the bacteriophage lambda exo gene (network). It encodes the lambda bacteriophage exonuclease.
SEQ ID NO: 14 shows the amino acid sequence of the bacteriophage lambda exonuclease.
The sequence is one of three identical subunits that are mounted on a trimer.
The enzyme performs highly processive digestion of nucleotides from a dsDNA strand, in a 5 'to 3' direction (http://www.neb.com/nebecomm/ products / productM0262.asp). The start of the enzyme in a filament preferably requires a 5 'projection of approximately 4 nucleotides with a 5' phosphate.
SEQ ID NOs: 15 to 17 show the amino acid sequence of the mature forms of the MspB, C and D mutants respectively.
The mature forms lack the signal sequence.
SEQ ID NOs: 18 to 32 show the sequences used in the Examples.
SEQ ID NO: 33 shows the polynucleotide sequence that encodes an α-HL-Q subunit.
SEQ ID NO: 34 shows the amino acid sequence of an α-HL-Q subunit.
SEQ ID NO: 35 shows the polynucleotide sequence that encodes a subunit of α-HL-E287C-QC-D5FLAGH6. SEQ ID NO: 36 shows the amino acid sequence of a subunit of α-HL-E287C-QC-D5FLAGH6. SEQ ID NO: 37 shows the polynucleotide sequence that encodes an α-hemolysin-E111N / K147N subunit (α-HL-NN;
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Stoddart et al., PNAS, 2009; 106 (19): 7702-7707). SEQ ID NO: 38 shows the amino acid sequence of an α-HL-NN subunit.
SEQ ID NO: 39 shows the sequence used in Example 5. SEQ ID NOs: 40 and 41 show the sequences used in Example 6. Detailed description of the invention It should be understood that different applications of the disclosed products and methods can be adapted to the specific technical needs.
It should also be understood that the terminology used here is only for the purpose of describing the particular embodiments of the invention, it should not be intended as a limitation.
In addition, as used in this specification and the appended claims, the singular forms "one", "one", and "o", "a" include plural referendums unless the content clearly dictates otherwise.
Thus, for example, reference to "one analyte" includes two or more analytes, reference to "one detector" includes two or more of such detectors, reference to "one pore" includes two or more of such pores, reference to "a sequence nucleic acid ”includes two or more such sequences, and the like.
All publications, patents and patent applications cited herein, whether above or below, are hereby incorporated by reference in their entirety.
Methods of the invention The invention provides a method for determining the presence, absence or characteristics of an analyte.
The method comprises attaching the analyte to a membrane and letting the analyte interact with a detector present in the membrane.
The presence, absence or characteristics of the analyte are thus determined.
In one embodiment, the invention provides a method for determining the presence or absence of an analyte, which comprises (a)
16/106 attach the analyte to a membrane and (b) let the analyte interact with a detector present on the membrane and thereby determine the presence or absence of the analyte.
As discussed above, attaching the analyte to a membrane containing the detector decreases the amount of analyte required by several orders of magnitude.
The method is naturally advantageous for detecting analytes that are present in low concentrations.
The method preferably allows the presence or characteristics of the analyte to be determined when the analyte is present in a concentration of about 0.001 pM to about 1 nM, such as less than 0.01 pM, less than 0.1 pM, less than 1 pM, less than 10 pM or less than 100 pM.
The method of the invention is particularly advantageous for nucleic acid sequencing because, as discussed above, only small amounts of purified nucleic acid can be obtained from human blood.
The method preferably allows to estimate the sequence of, or allows for the sequencing of, a target polynucleotide that is present in a concentration of about 0.001 pM to about 1 nM, such as less than 0.01 pM, less than 0, 1 pM, less than 1 pM, less than 10 pM or less than 100 pM.
Attaching one end of a polynucleotide to the membrane (even if temporarily) also means that the end will be prevented from interfering with the nanopore-based sequencing process.
This is discussed in more detail below with reference to the exonuclease Sequencing method of the invention.
The method of the invention may comprise determining or measuring one or more characteristics of an analyte, such as a polynucleotide.
The method may involve determining or measuring two, three, four or five or more characteristics of the analyte, such as a polynucleotide.
For polynucleotides, the one or more characteristics are preferably
17/106 selected from (i) the length of the target polynucleotide, (ii) the identity of the target polynucleotide, (iii) the sequence of the target polynucleotide, (iv) the secondary structure of the target polynucleotide and (v) whether the target polynucleotide is modified or not.
Any combination of (i) to (v) can be determined or measured according to the invention.
The method preferably comprises estimating the sequence or sequencing of a polynucleotide.
Analyte The analyte can be any substance.
Suitable analytes include, but are not limited to, metal ions, inorganic salts, polymers, such as a polymeric acid or base, dyes, brighteners, pharmaceuticals, diagnostic agents, recreational drugs, explosives and environmental pollutants.
The analyte can be an analyte that is secreted from the cells.
Alternatively, the analyte can be an analyte that is present within cells so that the analyte must be extracted from the cells before the invention can be carried out.
The analyte is preferably an amino acid, peptide, polypeptide, protein or polynucleotide.
The amino acid, peptide, polypeptide or protein can be naturally occurring or non-naturally occurring.
The polypeptide or protein may include synthetic or modified amino acids within them.
Several different types of modifications to amino acids are known in the art.
For the purposes of the invention, it should be understood that the analyte can be modified by any method available in the art.
The protein can be an enzyme, antibody, hormone, growth factor or growth regulating protein, such as a cytokine.
The cytokine can be selected from an interleukin, preferably IFN-1, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12 or IL-13, an interferon, preferably IL-γ or other cytokines such as TNF-α.
The protein can be a protein
18/106 bacterial, fungal protein, viral protein or parasite derived protein.
Before it is contacted with the pore or channel, the protein can be unfolded to form a polypeptide chain.
The analyte is most preferably a polynucleotide, such as a nucleic acid.
Polynucleotides are discussed in more detail below.
A polynucleotide can be attached to the membrane at its 5 'end or 3' end or at one or more intermediate points along the filament.
The polynucleotide can be single-stranded or double-stranded as discussed below.
The polynucleotide can be circular.
The polynucleotide can be an aptamer, a probe that hybridizes to the microRNA or the microRNA itself (Wang, Y. et al, Nature Nanotechnology, 2011, 6, 668-674). When the analyte is a probe that hybridizes to the microRNA, the probe can be attached permanently (Fig. 23A) or transiently (Fig. 23 B and C) to the membrane.
The probe itself can be adapted to bind directly to the membrane or it can hybridize to a complementary polynucleotide that has been adapted to bind to the membrane.
The analyte can be a microRNA complex hybridized to a probe where the probe has distinctive sequences or bar codes that allow it to be unambiguously identified.
When the analyte is an aptamer, the aptamer can be permanently or transiently attached to the membrane.
The aptamer itself can be adapted to bind directly to the membrane or it can hybridize to a complementary polynucleotide that has been adapted to bind to the membrane.
The aptamer can be linked or not linked to a protein analyte and the ultimate purpose of detecting the aptamer can be to detect the presence, absence or characteristics of a protein analyte to which it attaches.
The analyte is present in any suitable sample.
The invention is typically carried out on a sample that is known to contain or
19/106 suspected of containing the analyte.
The invention can be carried out on a sample containing one or more analytes whose identity is unknown.
Alternatively, the invention can be carried out on a sample to confirm the identity of one or more analytes whose presence in the sample is known or expected.
The sample can be a biological sample.
The invention can be carried out in vitro on a sample obtained from or extracted from any organism or microorganism.
The organism or microorganism is typically Archean, prokaryotic or eukaryotic and typically belongs to one of the five kingdoms: vegetable, animal, fungal, monera and protist.
The invention can be carried out in vitro on a sample obtained from or extracted from any virus.
The sample is preferably a fluid sample.
The sample typically comprises a patient's body fluid.
The sample may be urine, lymph, saliva, mucus or amniotic fluid but is preferably blood, plasma or serum.
Typically, the sample is human in origin, but alternatively it may be from another mammalian animal such as commercial farm animals such as horses, cattle, sheep or pigs or alternatively it may be pets such as cats or dogs.
Alternatively a sample of plant origin is typically obtained from a commercial crop, such as a cereal, vegetable, fruit or vegetable, for example wheat, barley, oats, canola, corn, soy, rice, bananas, apples, tomatoes, potatoes, grapes , tobacco, beans, lentils, sugar cane, cocoa, cotton.
The sample can be a non-biological sample.
The non-biological sample is preferably a fluid sample.
Examples of a non-biological sample include surgical fluids, water such as drinking water, sea water or river water, and reagents for laboratory tests.
The sample is typically processed before testing, for example by centrifugation or passing through a membrane that filters out unwanted molecules or cells, such as blood cells
20/106 red.
The sample can be measured immediately when collected.
The sample can also typically be stored before testing, preferably below -70 ° C.
Membrane Any membrane can be used according to the invention.
Suitable membranes are well known in the art.
The membrane is preferably an amphiphilic layer.
An amphiphilic layer is a layer formed of amphiphilic molecules, such as phospholipids, which have both hydrophilic and lipophilic properties.
Amphiphilic molecules can be synthetic or naturally occurring.
Non-naturally occurring amphiphiles and monolayer forming amphiphiles are known in the art and include, for example, block copolymers (Gonzalez-Perez et al., Langmuir, 2009, 25, 10447-10450). Block copolymers are polymeric materials in which two or more monomeric subunits are polymerized together to create a single polymeric chain.
Block copolymers typically have properties that are contributed by each monomeric subunit.
However, a block copolymer may have unique properties that polymers formed from individual subunits do not.
Block copolymers can be engineered so that one of the monomeric subunits is hydrophobic (i.e., lipophilic), while the other subunit (s) is / are hydrophilic (s) while in an aqueous medium.
In this case, the block copolymer can have amphiphilic properties and can form a structure that mimics a biological membrane.
The block copolymer can be a diblock (consisting of two monomeric subunits), but it can also be constructed from more than two monomeric subunits to form more complex arrangements that behave like amphiphiles.
The copolymer can be a triblock, tetrablock or pentablock copolymer.
Archaeobacterial bipolar tetraether lipids are of
21/106 naturally occurring lipids that are constructed so that the lipid forms a monolayer membrane.
These lipids are generally found in extremophiles that survive in harsh biological environments, thermophiles, halophils and acidophils.
It is believed that its stability derives from the fused nature of the final bilayer.
Block copolymer materials that mimic these biological entities are easy to build by creating a triblock polymer that has the overall hydrophilic-hydrophobic-hydrophilic motif.
This material can form monomeric membranes that behave similarly to lipid bilayers and cover a range of vesicle phase behaviors across laminar membranes.
The membranes formed from these triblock copolymers retain several advantages over biological lipid membranes.
Because the triblock copolymer is synthesized, the exact construction can be carefully controlled to provide the correct chain lengths and properties required to form membranes and interact with pores and other proteins.
Block copolymers can also be constructed from subunits that are not classified as lipid submaterials; for example, a hydrophobic polymer can be made from siloxane or other monomers not based on hydrocarbons.
The hydrophilic subsection of block copolymer may also have low protein binding properties, which allows the creation of a membrane that is highly resistant when exposed to crude biological samples.
This tip group unit can also be derived from non-classical lipid tip groups.
Triblock copolymer membranes also have increased mechanical and environmental stability compared to biological lipid membranes, for example a much higher operating temperature or pH range.
The synthetic nature of block copolymers provides
22/106 a platform for customizing polymer-based membranes for a wide range of applications.
In a preferred embodiment, the invention provides a method for determining the presence, absence or characteristics of an analyte, which comprises (a) attaching the analyte to a membrane comprising a triblock copolymer, optionally in which the membrane is modified to facilitate binding, and (b) let the analyte interact with a detector present in the membrane and thereby determine the presence, absence or characteristics of the analyte.
As discussed above, a triblock copolymer is a polymer formed from three different monomeric subunits.
Amphiphilic molecules can be chemically modified or functionalized to facilitate binding of the analyte.
The amphiphilic layer can be a monolayer or a bilayer.
The amphiphilic layer is typically planar.
The amphiphilic layer can be curved.
Amphiphilic membranes are typically naturally mobile, acting essentially as two dimensional fluids with lipid diffusion rates of approximately 10-8 cm s-1. This means that the detector and the bound analyte can typically move within an amphiphilic membrane.
The membrane is preferably a lipid bilayer.
Lipid bilayers are models of cell membranes and serve as excellent platforms for a range of experimental studies.
For example, lipid bilayers can be used for in vitro investigation of membrane proteins by single channel recording.
Alternatively, the lipid bilayers can be used as biosensors to detect the presence of a range of substances.
The lipid bilayer can be any lipid bilayer.
Suitable lipid bilayers include, but are not limited to, a lipid bilayer
23/106 planar, a sustained bilayer or a liposome.
The lipid bilayer is preferably a planar lipid bilayer.
Suitable lipid bilayers are disclosed in International Order No.
PCT / GB08 / 000563 (published as WO 2008/102121), International Application No.
PCT / GB08 / 004127 (published as WO 2009/077734) and International Order No.
PCT / GB2006 / 001057 (published as WO 2006/100484). Methods for forming lipid bilayers are known in the art.
Suitable methods are disclosed in the Example.
Lipid bilayers are usually formed by the method of Montal and Mueller (Proc.
Natl.
Acad.
Sci.
USA, 1972; 69: 3561-3566), in which a monolayer of lipid that is transported at the interface of the aqueous / air solution passes each side of an opening that is perpendicular to this interface.
The lipid is usually added to the surface of an aqueous electrolyte solution by first dissolving it in an organic solvent and then allowing a drop of the solvent to evaporate on the surface of the aqueous solution on each side of the opening.
Once the organic solvent has evaporated, the solution / air interfaces on each side of the opening are physically moved up and down past the opening until a bilayer is formed.
Planar lipid bilayers can be formed through an opening in a membrane or through an opening in a recess.
The Montal & Mueller method is popular because it is a cheap and relatively easy method of forming good quality lipid bilayers that are suitable for inserting protein into the pore.
Other common bilayer formation methods include tip dipping, painted bilayers and liposome bilayer patch-clamp.
The formation of bilayer with tip immersion necessarily involves touching the surface of the opening (for example, with a pipette tip) on the surface of a test solution that is carrying a lipid monolayer.
Again, the lipid monolayer is
24/106 first generated at the solution / air interface a drop of lipid dissolved in organic solvent is allowed to evaporate on the solution surface.
The bilayer is then formed by the Langmuir-Schaefer process and requires mechanical automation to move the opening relative to the solution's surface.
For painted bilayers, a drop of lipid dissolved in organic solvent is applied directly to the opening, which is submerged in an aqueous test solution.
The lipid solution is spread thinly over the opening using a brush or an equivalent.
Thinning of the solvent results in the formation of a lipid bilayer.
However, complete removal of the bilayer solvent is difficult and consequently the bilayer formed by this method is less stable and more prone to noise during electrochemical measurement.
The patch-clamp is commonly used in the study of biological cell membranes.
The cell membrane is attached to the end of a pipette by suction and a piece of the membrane is attached at the opening.
The method was adapted to produce lipid bilayers by stapling liposomes that then burst to leave a lipid bilayer sealing the pipette opening.
The method requires stable, giant and unilamellar liposomes and the manufacture of small openings in the materials having a glass surface.
Liposomes can be formed by sonification, extrusion or the Mozafari method (Colas et al. (2007) Micron 38: 841-847). In a preferred embodiment, the lipid bilayer is formed as described in International Application No.
PCT / GB08 / 004127 (published as WO 2009/077734). Advantageously in this method, the lipid bilayer is formed from dry lipids.
In a more preferred embodiment, the lipid bilayer is formed through an opening as described in WO2009 / 077734 (PCT / GB08 / 004127). A lipid bilayer is formed of two opposite layers
25/106 of lipids.
The two layers of lipids are arranged so that their hydrophobic tail groups are facing each other to form a hydrophobic interior.
The hydrophilic tip groups of the lipids facing out of the aqueous environment on each side of the bilayer.
The bilayer can be present in various lipid phases including, but not limited to, the liquid disordered phase (fluid lamellar), liquid ordered phase, solid ordered phase (lamellar gel phase, interdigitated gel phase) and planar bilayer crystals ( lamellar subgel, lamellar crystalline phase). Any lipid composition that forms a lipid bilayer can be used.
The lipid composition is chosen so that a lipid bilayer having the required properties, such as surface charge, ability to support membrane proteins, packing density or mechanical properties, is formed.
The lipid composition can comprise one or more different lipids.
For example, the lipid composition can contain up to 100 lipids.
The lipid composition preferably contains from 1 to 10 lipids.
The lipid composition can comprise naturally occurring lipids and / or artificial lipids.
Lipids typically comprise a tip group, an interfacial portion and two hydrophobic tail groups that can be the same or different.
Suitable tip groups include, but are not limited to, neutral tip groups, such as diacylglycerides (DG) and ceramides (CM); high-end zuiterionic groups, such as phosphatidylcholine (PC), phosphatidylethanolamine (PE) and sphingomyelin (SM); negatively charged tip groups, such as phosphatidylglycerol (PG); phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidic acid (PA) and cardiolipin (CA); and positively charged tip groups, such as trimethylammonium-propane (TAP). Suitable interfacial portions include, but are not limited to, naturally occurring interfacial portions, such as glycerol-based or ceramide-based moieties.
Suitable hydrophobic tail groups
26/106 include, but are not limited to, saturated hydrocarbon chains, such as lauric acid (n-dodecanolic acid), myristic acid (n-tetradeconic acid), palmitic acid (n-hexadecanoic acid), stearic acid (n- Octadecanoic) and Arachidic (n-Eicosanoic); unsaturated hydrocarbon chains, such as oleic acid (cis-9-Octadecanoic); and branched hydrocarbon chains, such as phytaneyl.
The length of the chain and the position and number of double bonds in unsaturated hydrocarbon chains can vary.
The length of the chains and the position and number of the branches, such as methyl groups, in the branched hydrocarbon chains can vary.
The hydrophobic tail groups can be attached to the interfacial portion as an ether or an ester.
Lipids can also be chemically modified.
The tip group or the tail group of the lipids can be chemically modified.
Suitable lipids whose tip groups have been chemically modified include, but are not limited to, PEG-modified lipids, such as 1,2-Diacil-sn-Glycerol-3-Phosphoethanolamine- N- [Methoxy (Polyethylene glycol) -2000] ; Functionalized PEG lipids, such as 1,2-Distearoil-sn-Glycerol-3 Phosphoethanolamine-N- [Biotinyl (Polyethylene glycol) 2000]; and modified lipids for conjugation, such as 1,2-Dioleoyl-sn-Glycero-3-Phosphoethanolamine-N- (succinyl) and 1,2-Dipalmitoyl-sn-Glycero-3 Phosphoethanolamine-N- (Biotinyl). Suitable lipids whose tail groups have been chemically modified include, but are not limited to, polymerizable lipids, such as 1,2-bis (10,12-tricosadiinoyl) -sn-Glycero-3-Phosphocholine; fluorinated lipids, such as 1-Palmitoyl-2- (16-Fluoropalmitoyl) - sn-Glycero-3-Phosphocholine; deuterated lipids, such as 1,2-Dipalmitoyl-D62-sn-Glycero-3-Phosphocholine; and ether-linked lipids, such as 1,2-Di-O-phytanyl-sn-Glycero-3-Phosphocholine.
The lipids can be chemically modified or functionalized to facilitate binding of the analyte.
The amphiphilic layer, for example the lipid composition,
27/106 typically comprises one or more additives that will affect the properties of the layer.
Suitable additives include, but are not limited to, fatty acids, such as palmitic acid, myristic acid and oleic acid; fatty alcohols, such as palmitic alcohol, myristic alcohol and oleic alcohol; sterols, such as cholesterol, ergosterol, lanosterol, sitosterol and stigmasterol; lysophospholipids, such as 1-Acyl-2-Hydroxy-sn-Glycero-3-Phosphocholine; and ceramides.
In another preferred embodiment, the membrane is a layer in the solid state.
A solid state layer is not of biological origin.
In other words, a solid state layer is not derived from or isolated from a biological environment such as an organism or cell, or a synthetically fabricated version of a biologically available structure.
Solid-state layers can be formed from both organic and inorganic materials including, but not limited to, microelectronic materials, insulating materials such as Si3N4, Al2O3, and SiO, organic and inorganic polymers such as polyamide, plastics such as Teflon® or elastomers such as two-component addition curing silicone rubber, and glasses.
The solid state layer can be formed from graphene.
Suitable graphene layers are disclosed in International Order No.
PCT / US2008 / 010637 (published as WO 2009/035647). Binding The analyte can be bound to the membrane using any known method.
If the membrane is an amphiphilic layer, such as a lipid bilayer, the analyte is preferably attached to the membrane via a polypeptide present on the membrane or a hydrophobic anchor present on the membrane.
The hydrophobic anchor is preferably a lipid, fatty acid, sterol, carbon nanotube, polypeptide, protein or amino acid, for example cholesterol, palmitate or tocopherol.
In preferred embodiments, the
28/106 analyte is not connected to the membrane via the detector.
Membrane components, such as amphiphilic molecules or lipids, can be chemically modified or functionalized to facilitate binding of the analyte to the membrane directly or via one or more ligands.
Examples of suitable chemical modifications and suitable modes of functionalization of the membrane components are discussed in more detail below.
Any proportion of the membrane components can be functionalized, for example at least 0.01%, at least 0.1%, at least 1%, at least 10%, at least 25%, at least 50% or 100%. The analyte can be attached directly to the membrane.
The analyte can be attached directly to the membrane at one or more, such as 2, 3, 4 or more, points.
The analyte is preferably attached to the membrane via a linker.
The analyte can be attached to the membrane via one or more, such as 2, 3, 4 or more, ligands.
A linker can bind more than one, such as 2, 3, 4 or more, analytes to the membrane.
The analyte can be attached to the membrane directly at one or more points and via one or more ligands.
Preferred linkers include, but are not limited to, polymers, such as polynucleotides, polyethylene glycols (PEGs), polysaccharides and polypeptides.
These linkers can be linear, branched or circular.
For example, the linker can be a circular polynucleotide.
If the analyte is itself a polynucleotide, it can hybridize to a complementary sequence in the circular polynucleotide ligand.
Functionalized ligands and the ways in which they can bind molecules are known in the art.
For example, linkers functionalized with maleimide groups will react with and bind to the cysteine residues in proteins.
In the context of this invention, the protein
29/106 may be present in the membrane, may be the analyte itself, or may be used to bind to the analyte.
This is discussed in more detail below.
Crosslinking of analytes can be avoided by using a “lock and key” arrangement. Only one end of each linker can react together to form a longer linker and the other ends of the linker each react with the analyte or membrane respectively.
Such binders are described in International Application No.
PCT / GB10 / 000132 (published as WO 2010/086602). The use of a linker is preferred in the sequencing embodiments discussed below.
If a polynucleotide analyte is permanently attached directly to the membrane, then some sequence data will be lost since the sequencing round cannot continue to the end of the polynucleotide due to the distance between the membrane and the detector.
If a linker is used, then the polynucleotide analyte can be processed until completion.
The connection can be permanent or stable.
In other words, the bond can be such that the analyte remains attached to the membrane during the method.
The connection can be transient.
In other words, the bond can be such that the analyte separates from the membrane during the method.
For certain applications, such as aptamer detection, the transient nature of the bond is preferred.
If a permanent or stable ligand is attached directly to the 5 'or 3' end of a polynucleotide and the ligand is shorter than the distance between the bilayer and the nanopore channel or the binding protein of the polynucleotide's active site, then some sequence data will be lost since the sequencing round cannot continue to the end of the polynucleotide.
If the bond is transient, then when the bonded end randomly becomes free of the bilayer, then the polynucleotide can be processed until completion.
Chemical groups that form permanent / stable or transient bonds with the membrane are discussed in more detail below. THE
30/106 analyte can be transiently linked to an amphiphilic layer or lipid bilayer using cholesterol or an acyl grease chain.
Any chain of acyl grease having a length of 6 to 30 carbon atoms, such as hexadecanoic acid, can be used.
In preferred embodiments, a polynucleotide analyte, such as a nucleic acid, is attached to an amphiphilic layer such as a lipid bilayer.
The attachment of nucleic acids to synthetic lipid bilayers has previously been accomplished with several different mooring strategies.
These are summarized in Table 3 below.
Table 3 Connection group Type of connection Reference Stable Tiol Yoshina-Ishii, C. and S. G.
Boxer (2003). "Arrays of mobile tethered vesicles on supported lipids bilayer." J Am Chem Soc 125 (13): 3696-7. Stable Biotin Nikolov, V., R.
Lipowsky, et al. (2007). "Behavior of giant vesicles with anchored DNA molecules." Biophys J 92 (12): 4356-68 Transitory Colestrol Pfeiffer, I. and F.
Hook (2004). "Bivalent cholesterol-based coupling of oligonucletides to lipid membrane assemblies." J Am Chem Soc 126 (33): 10224-5 Surfactant (by Stable van Lengerich, B., R. J.
Rawle, et al. "Covalent example, Lipid, attachment of lipid vesicles to a fluid-supported Palmitate, etc.) bilayer allows observation of DNA-mediated vesicle interactions." Langmuir 26 (11): 8666-72
Analytes or synthetic polynucleotide ligands can be functionalized using a modified phosphoramidite in the synthesis reaction, which is easily compatible for the direct addition of suitable binding moieties, such as cholesterol, tocopherol or palmitate, as well as for reactive groups, such as thiol groups , cholesterol, lipid and biotin.
These different binding chemicals give a group of options for binding to target polynucleotides.
Each different modification group ties the polynucleotide in a slightly different way and the bond is not always permanent, thus giving different residence times for the analyte to the bilayer.
The advantages of transient linking are discussed above.
The attachment of polynucleotides to a ligand or to a functionalized membrane can also be achieved by several other means
31/106 as long as a complementary reactive group or a mooring can be added to the target polynucleotide.
The addition of reactive groups to each end of DNA has been reported previously.
A thiol group can be added to the 5 'of ssDNA or dsDNA using T4 polynucleotide kinase and ATPγS (Grant, G.
P. and P. Z.
Qin (2007). “A facile method for attaching nitroxide spin labels at the 5’ terminus of nucleic acids. ” Nucleic Acids Res 35 (10): e77). An azide group can be added to the ssDNA or dsDNA 5'-phosphate using T4 polynucleotide kinase and γ- [2-Azidoethyl] -ATP or γ- [6- Azidohexyl] -ATP.
Using thiol or Click chemistry, a mooring, which contains a thiol group, iodoacetamide OPSS or maleimide (reactive for thiols) or a DIBO (dibenzocyclooxtin) or alkaline group (reactive for azides), can be covalently linked to the analyte.
A more diverse selection of chemical groups, such as biotin, thiols and fluorophores, can be added using terminal transferase to incorporate modified oligonucleotides to the 3 'ssDNA (Kumar, A., P.
Tchen, et al. (1988). "Nonradioactive labeling of synthetic oligonucleotides probes with terminal deoxynucleotidil transferase." Anal Biochem 169 (2): 376-82). Example 3 below describes how DNA can be linked to a lipid bilayer using streptavidin / biotin.
The streptavidin / biotin binding can be used for any other analyte.
It may also be possible that lashings can be directly added to target polynucleotides using terminal transferase with suitably modified nucleotides (for example, cholesterol or palmitate). Alternatively, the reactive or mooring group can be considered to be the addition of a short piece of polynucleotide, such as DNA, complementary to one already linked to the bilayer, so that the bond can be obtained through hybridization.
In this case, the reactive group can be a single-stranded or double-stranded polynucleotide.
The reactive group can be attached to a single-stranded polynucleotide analyte or
32/106 double filament.
Binding of short pieces of ssDNA has been reported using T4 RNA ligase I (Troutt, A. B., M. G.
McHeyzer-Williams, et al. (1992). “Ligation-anchored PCR: a simple amplification technique with single-sided specificity.” Proc Natl Acad Sci U S A 89 (20): 9823-5). Alternatively, ssDNA or dsDNA can be linked to the dsDNA of the native analyte and then the two strands separated by thermal or chemical denaturation.
To native dsDNA, you can add a piece of ssDNA to one or both ends of the duplex, or dsDNA to either or both ends.
As for the addition of single stranded nucleic acids to native DNA this can be achieved using T4 RNA ligase I as for binding to other regions of single stranded nucleic acids.
For the addition of dsDNA to the native duplex DNA then the binding can be "abruptly terminated", with the complementary 3 'dA / dT tails on the native DNA and adapter respectively (as is routinely done for many sample preparation applications to prevent formation of concatomer or dimer) or using “sticky ends” generated by restriction digestion of native DNA and binding of compatible adapters.
Then, when the duplex is fused, each single strand will have a 5 'or 3' modification if ssDNA was used for ligation or a modification at the 5 'end, at the 3' end or both if dsDNA was used for ligation.
If the polynucleotide is a synthetic filament, the bonding chemistry can be incorporated during the chemical synthesis of the polynucleotide.
For example, the polynucleotide can be synthesized using a primer having a reactive group attached to it.
Adenylated nucleic acids (AppDNA) are intermediates in binding reactions, where an adenosine monophosphate is attached to the 5'-phosphate of the nucleic acid.
Several kits are available for the generation of this intermediate, such as the NEB 5 'DNA Adenylation Kit.
By replacing ATP in the reaction with a modified nucleotide triphosphate,
33/106 then the addition of reactive groups (such as thiols, amines, biotin, azides, etc.) to the 5 'of DNA should be possible.
It may also be possible that the ties can be directly added to the target polynucleotides using a 5 'DNA adenylation kit with suitably modified nucleotides (eg, cholesterol or palmitate). A common technique for amplifying sections of genomic DNA is to use the polymerase chain reaction (PCR). Here, using two synthetic oligonucleotide primers, several copies of the same section of DNA can be generated, where for each copy 5 'of each strand in the duplex will be a synthetic polynucleotide.
By using a single or multiple nucleotide antisense primer, the 3 'end of single or double stranded DNA can be added by the use of a polymerase.
Examples of polymerases that can be used include, but are not limited to, Terminal Transferase, Klenow and Poly (a) E. coli Polymerase). By replacing ATP in the reaction with a modified nucleotide triphosphate then reactive groups, such as a cholesterol, thiol, amine, azide, biotin or lipid, can be incorporated into the DNA.
Therefore, each copy of the target amplified DNA will contain a reactive group for ligation.
Ideally, the analyte is attached to the membrane without having to functionalize the analyte.
This can be achieved by anchoring a linking group, such as a protein that binds polynucleotide or a chemical group, to the membrane and letting the linking group interact with the analyte or by functionalizing the membrane.
The linking group can be attached to the membrane by any of the methods described herein.
In particular, the linking group can be attached to the membrane using one or more linkers, such as maleimide functionalized linkers.
In this embodiment, the analyte is typically RNA, DNA, PNA, TNA or LNA and can be double or single stranded.
This embodiment is particularly adapted for genomic DNA analytes.
34/106
The linking group can be any group that interacts with single or double-stranded nucleic acids, specific nucleotide sequences within the analyte or modified nucleotide patterns within the analyte, or any other ligand that is present in the polynucleotide.
Suitable binding proteins include the E. coli single strand binding protein, P5 single strand binding protein, T4 gp32 single strand binding protein, the dsDNA topV binding region, human histone proteins, HU binding protein E. coli DNA and other proteins that bind archaic, prokaryotic or eukaryotic single or double-stranded nucleic acid, including those listed below.
The specific nucleotide sequences can be sequences recognized by transcription factors, ribosomes, endonucleases, topoisomerases or initiation of replication factors.
The modified nucleotide patterns can be methylation or damage patterns.
The chemical group can be any group that intercalates with or interacts with a polynucleotide analyte.
The group can intercalate or interact with the polynucleotide analyte through electrostatic, hydrogen bonding or Van der Waals interactions.
Such groups include a lysine monomer, poly-lysine (which will interact with ssDNA or dsDNA), ethidium bromide (which will intercalate with dsDNA), universal bases or universal nucleotides (which can hybridize to any polynucleotide analyte) and osmium complexes ( that can react with methylated bases). A polynucleotide analyte can therefore be attached to the membrane using one or more universal nucleotides attached to the membrane.
Each universal nucleotide residue can be attached to the membrane using one or more ligands.
Examples of universal bases include inosine, 3-nitropyrrole, 5-nitroindole, 4-nitroindole, 6-nitroindole, 3,4-dihydro-pyrimido [4,5-c] [1,2] oxazin-7-one (dP), 2-dimethylaminomethyleneamino-6-methyloxyaminopurine (dK), deoxy inosine, deoxy nebularin.
35/106
In this embodiment at least 1%, at least 10%, at least 25%, at least 50% or 100% of the membrane components can be functionalized.
Where the linking group is a protein, it may be able to anchor directly within the membrane without additional functionalization, for example if it already has an external hydrophobic region that is compatible with the membrane.
Examples of such proteins include transmembrane proteins.
Alternatively, the protein can be expressed with a genetically fused hydrophobic region that is compatible with the membrane.
Such hydrophobic protein regions are known in the art.
The linking group is preferably mixed with the analyte prior to contact with the membrane, but the linking group can be contacted with the membrane and subsequently contacted with the analyte.
In another aspect, the analyte can be functionalized, using the methods described above, so that it can be recognized by a specific linking group.
Specifically, the analyte can be functionalized with a ligand such as biotin (to bind streptavidin), amylose (to bind to the maltose binding protein or a fusion protein), Ni-NTA (to bind to poly- histidine or proteins targeted by polyhistidine) or a peptide (such as an antigen). According to another aspect, the linking group can be used to attach polynucleotide analyte to the membrane when the analyte is attached to a polynucleotide adapter .
Specifically, the analyte binds to an adapter that comprises a leader sequence designed to preferably insert into a detector such as a nanopore.
Such a leader sequence can comprise a homopolymeric polynucleotide or an abasic region.
The adapter is typically designed to hybridize to a ligand and bind or hybridize to the analyte.
This creates competition between the analyte and the adapter to enter the detector.
If the linker comprises a group of
36/106 binding, the length of the longer analyte compared to the adapter means that several ligands can bind to the analyte simultaneously, thereby increasing the concentration of analyte over that of the adapter.
Any of the methods discussed above for attaching polynucleotides to amphiphilic layers, such as lipid bilayers, can naturally be applied to other analyte and membrane combinations.
In some embodiments, an amino acid, peptide, polypeptide or protein is linked to a lipid bilayer.
Various methodologies for the chemical bonding of such analytes are available.
An example of a molecule used in chemical bonding is EDC (1-ethyl-3- [3-dimethylaminopropyl] carbodiimide hydrochloride). Reactive groups can also be added to 5 'of DNA using commercially available kits (Thermo Pierce, Part No. 22980). Suitable methods include, but are not limited to, transient affinity binding using histidine residues and NITTA, as well as more robust covalent bonds by reactive cysteines, lysines or unnatural amino acids.
Detector The detector can be any structure that provides a readable signal in response to the presence, absence or characteristics of the analyte.
The detector can be any structure that provides a readable signal in response to the presence or absence of the analyte.
Suitable detectors are known in the art.
They include, but are not limited to, transmembrane pores, tunneling electrodes, class electrodes, nanotubes, FETs (field effect transistors) and optical detectors, such as atomic force microscopes (AFMs) and scanning tunneling microscopes ( STMs). In preferred embodiments, the detector detects the analyte using electrical means.
Electrical measurements can be made using standard single channel recording equipment as described in Stoddart D et al., Proc Natl Acad Sci, 12; 106 (19): 7702-7, Lieberman KR et al, J Am
37/106
Chem Soc. 2010; 132 (50): 17961-72, and International Application WO-2000/28312. Alternatively, electrical measurements can be made using a multichannel system, for example as described in International Application WO-2009/077734 and International Application WO-2011/067559. In other preferred embodiments, the detector does not detect the analyte using fluorescent means.
The detector preferably comprises a transmembrane portion.
A transmembrane pore is a structure that allows hydrated ions driven by an applied potential to flow from one side of the membrane to the other side of the membrane.
The transmembrane pore is preferably a transmembrane protein pore.
A transmembrane protein pore is a polypeptide or collection of polypeptides that allows hydrated ions, such as the analyte, to flow from one side of a membrane to the other side of the membrane.
In the present invention, the transmembrane protein pore is able to form a pore that allows hydrated ions driven by an applied potential to flow from one side of the membrane to the other.
The transmembrane protein pore preferably allows the analyte such as nucleotides to flow from one side of the membrane, such as a lipid bilayer, to the other.
The transmembrane protein pore preferably allows a polynucleotide or nucleic acid, such as DNA or RNA, to move through the pore.
The transmembrane protein pore can be a monomer or an oligomer.
The pore is preferably made up of several repeating subunits, such as 6, 7 or 8 subunits.
The pore is more preferably a heptameric or octameric pore.
The transmembrane protein pore typically comprises a tube or channel through which ions can flow.
The pore subunits typically surround a central axis and contribute filaments to a
38/106 transmembrane β tube or channel or a transmembrane α helix beam or channel.
The transmembrane protein pore tube or channel typically comprises amino acids that facilitate interaction with the analyte, such as nucleotides, polynucleotides or nucleic acids.
These amino acids are preferably located close to a tube or channel constriction.
The transmembrane protein pore typically comprises one or more positively charged amino acids, such as arginine, lysine or histidine, or aromatic amino acids, such as tyrosine or tryptophan.
These amino acids typically facilitate the interaction between the pore and the nucleotides, polynucleotides or nucleic acids.
Nucleotide detection can be facilitated with an adapter.
This is discussed in more detail below.
The transmembrane protein pores for use according to the invention can be derived from β tube pores or α helix beam pores.
The β tube pores comprise a tube or channel that is formed from β filaments.
Suitable β-tube pores include, but are not limited to, β toxins, such as α hemolysin, anthrax toxin and leukocidins, and bacterial sternal membrane / porin proteins, such as Mycobacterium smegmatis (Msp) porine, for example MspA, MspB, MspC or MspD, external membrane porin F (OmpF), external membrane porin G (OmpG), external membrane phospholipase A and Neisseria autotransporter lipoprotein (NalP). The helix beam pores α comprise a tube or channel that is formed of α helices.
Suitable α helix beam pores include, but are not limited to, inner membrane proteins and outer membrane proteins α, such as toxins WZA and ClyA.
The transmembrane pore can be derived from Msp or α-hemolysin (α-HL). For filament sequencing, the protein pore of
39/106 transmembrane is preferably derived from Msp, preferably from MspA.
Such a pore will be oligomeric and typically comprises 7, 8, 9 or 10 monomers derived from Msp.
The pore may be a homologous pore derivative of Msp that comprises identical monomers.
Alternatively, the pore can be a hetero-oligomeric pore derived from Msp that comprises at least one monomer that differs from the others.
The pore can also comprise one or more constructs comprising two or more covalently linked monomers derived from Msp.
Suitable pores are disclosed in International Order No.
PCT / GB2012 / 050301 (which claims priority for US Provisional Application No. 61 / 441,718). Preferably the pore is derived from MspA or a homologous or analogous to it.
A monomer derived from Msp comprises the sequence shown in SEQ ID NO: 2 or a variant thereof.
SEQ ID NO: 2 is the NNN-RRK mutant of the monomer MspA.
It includes the following mutations: D90N, D91N, D93N, D118R, D134R and E139K.
A variant of SEQ ID NO: 2 is a polypeptide that has an amino acid sequence that varies from that of SEQ ID NO: 2 and that retains its ability to form a pore.
The ability of a variant to form a pore can be tested using any method known in the art.
For example, the variant can be inserted into a lipid bilayer together with other appropriate subunits and its ability to oligomerize to form a pore can be determined.
Methods are known in the art for inserting subunits within membranes, such as lipid bilayers.
For example, subunits can be suspended in a purified form in a solution that contains a lipid bilayer so that it diffuses to the lipid bilayer and is inserted by binding to the lipid bilayer and assembling within a state functional.
Alternatively, subunits can be directly inserted into the
40/106 membrane using the pick and place method described in M. THE.
Holden, H.
Bailey. J.
Am.
Chem.
Soc. 2005, 127, 6502-6503 and International Order No.
PCT / GB2006 / 001057 (published as WO 2006/100484). Preferred variants are disclosed in International Order No.
PCT / GB2012 / 050301 (which claims priority for US Provisional Application No. 61 / 441,718). Particularly preferred variants include, but are not limited to, those comprising the following substitution (s): L88N; L88S; L88Q; L88T; D90S; D90Q; D90Y; I105L; I105S; Q126R; G75S; G77S; G75S, G77S, L88N and Q126R; G75S, G77S, L88N, D90Q and Q126R; D90Q and Q126R; L88N, D90Q and Q126R; L88S and D90Q; L88N and D90Q; E59R; G75Q; G75N; G75S; G75T; G77Q; G77N; G77S; G77T; I78L; S81N; T83N; N86S; N86T; I87F; I87V; I87L; L88N; L88S; L88Y; L88F; L88V; L88Q; L88T; I89F; I89V; I89L; N90S; N90Q; N90L; N90Y; N91S; N91Q; N91L; N91M; N91I; N91A; N91V; N91G; G92A; G92S; N93S; N93A; N93T; I94L; T95V; A96R; A96D; A96V; A96N; A96S; A96T; P97S; P98S; F99S; G100S; L101F; N102K; N102S; N102T; S103A; S103Q; S103N; S103G; S103T; V104I; I105Y; I105L; I105A; I105Q; I105N; I105S; I105T; T106F; T106I; T106V; T106S; N108P; N108S; D90Q and I105A; D90S and G92S; L88T and D90S; I87Q and D90S; I89Y and D90S; L88N and I89F; L88N and I89Y; D90S and G92A; D90S and I94N; D90S and V104I; L88D and I105K; L88N and Q126R; L88N, D90Q and D91R; L88N, D90Q and D91S; L88N, D90Q and I105V; D90Q, D93S and I105A; N91Y; N90Y and N91G; N90G and N91Y; N90G and N91G; I05G; N90R; N91R; N90R and N91R; N90K; N91K; N90K and N91K; N90Q and N91G; N90G and N91Q; N90Q and N91Q; R118N; N91C; N90C; N90W; N91W; N90K; N91K; N90R; N91R; N90S and N91S; N90Y and I105A; N90G and I105A; N90Q and I105A; N90S and I105A; L88A and I105A; L88S and I105S; L88N and I105N; N90G and N93G; N90G; N93G; N90G and N91A; I105K; I105R; I105V; I105P; I105W; L88R; L88A; L88G; L88N; N90R and I105A; N90S and I105A; L88A and I105A; L88S and I105S; L88N and I105N; L88C; S103C; and I105C.
41/106
In addition to the specific mutations discussed above, the variant may include other mutations.
Over the entire length of the amino acid sequence of SEQ ID NO: 2, a variant will preferably be at least 50% homologous to this sequence based on the amino acid identity.
More preferably, the variant can be at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90% and more preferably at least 95%, 97% or 99% homologous based on the amino acid identity to the amino acid sequence of SEQ ID NO: 2 with respect to the entire sequence.
There can be at least 80%, for example at least 85%, 90% or 95%, of amino acid identity with respect to a stretch of 100 or more, for example 125, 150, 175 or 200 or more, contiguous amino acids (“ difficult homology ”). Standard methods in the art can be used to determine homology.
For example, the UWGCG Package provides the BESTFIT program that can be used to calculate homology, for example used in its default settings (Devereux et al (1984) Nucleic Acids Research 12, p387-395). The PILEUP and BLAST algorithms can be used to calculate homology or sequence alignment (such as identifying equivalent residues or corresponding sequences (typically in your default settings)), for example as described in Altschul S.
F. (1993) J Mol Evol 36: 290-300; Altschul, S.
F et al (1990) J Mol Biol 215: 403-10. The software for performing BLAST analysis is publicly available through the National Center for Biotechnology Information (http: //www.ncbi.nlm. Nih.gov/). SEQ ID NO: 2 is the NNN-RRK mutant of the monomer MspA.
The variant can comprise any of the mutations in the MspB, C or D monomers compared to MspA.
The mature forms of MspB, C and D are shown in SEQ ID NOs: 15 to 17. In particular, the variant can comprise the following substitution present in MspB:
42/106
A138P.
The variant may comprise one or more of the following substitutions present in MspC: A96G, N102E and A138P.
The variant may comprise one or more of the following mutations present in MspD: G1, L2V, E5Q, L8V, D13G, W21A, D22E, K47T, I49H, I68V, D91G, A96Q, N102D, S103T, V104I, S136K and G141A deletion .
The variant may comprise combinations of one or more of the Msp B, C and D mutations and substitutions.
Amino acid substitutions can be made to the amino acid sequence of SEQ ID NO: 2 in addition to those discussed above, for example up to 1, 2, 3, 4, 5, 10, 20 or 30 substitutions.
Conservative substitutions replace amino acids with other amino acids of similar chemical structure, similar chemical properties or similar side chain volume.
The amino acids introduced can have similar polarity, hydrophilicity, hydrophobicity, basicity, acidity, neutrality or charge to the amino acids they replace.
Alternatively, conservative substitution can introduce another amino acid that is aromatic or aliphatic in place of a pre-existing aromatic or aliphatic amino acid.
Conservative amino acid changes are well known in the art and can be selected according to the properties of the 20 major amino acids as defined in Table 4 below.
Where the amino acids have similar polarity, this can also be determined by reference to the hydropathy scale for the amino acid side chains in Table 5. Table 4 - Chemical properties of the amino acids Aliphatic, hydrophobic, neutral Met hydrophobic, neutral Polar, hydrophobic Cys, neutral Asn polar, hydrophilic, neutral Asp polar, hydrophilic, charged (-) Pro hydrophobic, neutral Glu polar, hydrophilic, charged (-) Polar gln, hydrophilic, neutral Phe aromatic, hydrophobic, neutral Arg polar, hydrophilic, charged (+) Aliphatic Gly, neutral Polar, hydrophilic, neutral His aromatic, polar, hydrophilic, Thr polar, hydrophilic, neutral charged (+) Aliphatic, hydrophobic, neutral Aliphatic, hydrophobic, neutral Val polar, hydrophilic, charged (+) Aromatic trp , hydrophobic, neutral Leu aliphatic, hydrophobic, neutral Tyr aromatic, polar, hydrophobic
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Table 5 - Hydropathy Scale Side Chain Hydropathy Ile 4.5 Val 4.2 Leu 3.8 Phe 2.8 Cys 2.5 Met 1.9 Ala 1.8 Gly -0.4 Thr -0.7 Ser -0 .8 Trp -0.9 Tyr -1.3 Pro -1.6 His -3.2 Glu -3.5 Gln -3.5 Asp -3.5 Asn -3.5 Lys -3.9 Arg -4 , 5
One or more amino acid residues of the amino acid sequence of SEQ ID NO: 2 can be further deleted from the polypeptides described above.
Up to 1, 2, 3, 4, 5, 10, 20 or 30 residues can be deleted, or more.
Variants can include fragments of SEQ ID NO: 2. Such fragments retain activity that forms pore.
The fragments can be at least 50, 100, 150 or 200 amino acids in length.
Such fragments can be used to produce pores.
A fragment preferably comprises the pore-forming domain of SEQ ID NO: 2. The fragments must include one of residues 88, 90, 91, 105, 118 and 134 of SEQ ID NO: 2. Typically, the fragments include all residues 88 , 90, 91, 105, 118 and 134 of SEQ ID NO: 2. One or more amino acids can be an alternative or
44/106 additionally added to the polypeptides described above.
An extension can be provided at the amino or carboxy terminal of the amino acid sequence of SEQ ID NO: 2 or variant of polypeptide or fragment thereof.
The length can be very short, for example 1 to 10 amino acids in length.
Alternatively, the extension can be longer, for example up to 50 or 100 amino acids.
A carrier protein can be fused to an amino acid sequence according to the invention.
Other fusion proteins are discussed in more detail below.
As discussed above, a variant is a polypeptide that has an amino acid sequence that varies from that of SEQ ID NO: 2 and that retains its ability to form a pore.
A variant typically contains the regions of SEQ ID NO: 2 that are responsible for pore formation.
The pore-forming ability of Msp, which contains a β tube, is provided by the β leaves in each subunit.
A variant of SEQ ID NO: 2 typically comprises the regions in SEQ ID NO: 2 that form β sheets.
One or more modifications can be made to the regions of SEQ ID NO: 2 that form β sheets as long as the resulting variant retains its ability to form a pore.
A variant of SEQ ID NO: 2 preferably includes one or more modifications, such as substitutions, additions or deletions, within its α helices and / or loop regions.
Msp-derived monomers can be modified to aid in their identification or purification, for example by adding histidine residues (a hist tag), aspartic acid residues (an asp tag), a strraptavidin tag or a signal tag, or by adding a signal sequence to promote its secretion from a cell where the polypeptide does not naturally contain such a sequence.
An alternative to introducing a genetic tag is to chemically react a tag in a native or engineered position in the pore.
An example of this would be to react a reagent that changes to gel with a
45/106 cysteine generated outside the pore.
This has been demonstrated as a method to separate hetero-oligomers from hemolysin (Chem Biol.
Jul 1997; 4 (7): 497-505). The Msp-derived monomer can be labeled with a developer tag.
The developer tag can be any suitable tag that allows the pore to be detected.
Suitable labels include, but are not limited to, fluorescent molecules, radioisotopes, for example, I, 35S, enzymes, antibodies, antigens, polynucleotides and ligands such as biotin.
The Msp-derived monomer can also be produced using D-amino acids.
For example, the Msp-derived monomer can comprise a mixture of L-amino acids and D-amino acids.
This is conventional in the art to produce such proteins or peptides.
The Msp-derived monomer contains one or more specific modifications to facilitate nucleotide discrimination.
The Msp-derived monomer can also contain other non-specific modifications as long as they do not interfere with pore formation.
Various non-specific side chain modifications are known in the art and can be made to the side chains of the Msp-derived monomer.
Such modifications include, for example, reductive alkylation of amino acids by reaction with an aldehyde followed by reduction with NaBH4, amidination with methylacetimidate or acylation with acetic anhydride.
The Msp-derived monomer can be produced using standard methods known in the art.
The Msp-derived monomer can be manufactured synthetically or by recombinant means.
For example, the pore can be synthesized by in vitro translation and transcription (IVTT). Suitable methods for producing pores are discussed in International Order Nos.
PCT / GB09 / 001690 (published as WO 2010/004273), PCT / GB09 / 001679 (published as WO 2010/004265) or
46/106
PCT / GB10 / 000133 (published as WO 2010/086603). Methods for inserting pores into membranes are discussed below.
For Exonuclease Sequencing, the transmembrane protein pore is preferably derived from α-hemolysin (α-HL). The pore of wild-type α-HL is formed from seven identical monomers or subunits (that is, it is heptameric). The sequence of an M113R α-hemolysin monomer or subunit is shown in SEQ ID NO: 4. The transmembrane protein pore preferably comprises seven monomers each comprising the sequence shown in SEQ ID NO: 4 or a variant thereof.
Amino acids 1, 7 to 21, 31 to 34, 45 to 51, 63 to 66, 72, 92 to 97, 104 to 111, 124 to 136, 149 to 153, 160 to 164 , from 173 to 206, from 210 to 213, 217, 218, from 223 to 228, from 236 to 242, from 262 to 265, from 272 to 274, from 287 to 290 and 294 of SEQ ID NO: 4 form regions of shoulder strap.
Residues 113 and 147 of SEQ ID NO: 4 form part of a constriction of the α-HL tube or channel.
In such embodiments, a pore comprising seven proteins or monomers each comprising the sequence shown in SEQ ID NO: 4 or a variant thereof is preferably used in the method of the invention.
The seven proteins can be the same (homoheptamer) or different (heteroheptamer). A variant of SEQ ID NO: 4 is a protein that has an amino acid sequence that varies from that of SEQ ID NO: 4 and that retains its pore-forming ability.
The ability of a variant to form a pore can be tested using any method known in the art.
For example, the variant can be inserted into a lipid bilayer together with other appropriate subunits and its ability to oligomerize to form a pore can be determined.
Methods are known in the art for inserting subunits within membranes, such as lipid bilayers.
The appropriate methods are discussed above.
47/106 The variant may include modifications that facilitate covalent binding to or interaction with a protein that binds nucleic acid. The variant preferably comprises one or more reactive cysteine residues that facilitate binding to the protein that binds nucleic acid. For example, the variant may include a cysteine in one or more of positions 8, 9, 17, 18, 19, 44, 45, 50, 51, 237, 239 and 287 and / or at the amino or carboxy terminus of SEQ ID NO :
4. Preferred variants comprise a replacement of the residue in positions 8, 9, 17, 237, 239 and 287 of SEQ ID NO: 4 with cysteine (A8C, T9C, N17C, K237C, S239C or E287C). The variant is preferably any of the variants described in International Application No. PCT / GB09 / 001690 (published as WO 2010/004273), PCT / GB09 / 001679 (published as WO 2010/004265) or PCT / GB10 / 000133 (published as WO 2010/086603). The variant can also include modifications that facilitate any interaction with nucleotides or facilitate the orientation of a molecular adapter as discussed below. The variant may also contain modifications that facilitate the covalent attachment of a molecular adapter. In particular, the variant preferably contains a glutamine at position 139 of SEQ ID NO: 4. The variant preferably has a cysteine at position 119, 121 or 135 of SEQ ID NO: 4. A variant of SEQ ID NO: 4 can have the wild type methionine reintroduced at position 113. Preferred variants of SEQ ID NO: 4 have a methionine at position 113 (R113M), a cysteine at position 135 (L135C) and a glutamine at position 139 (N139Q). Other preferred variants of SEQ ID NO: 4 have a methionine at position 113 (R113M) and a glutamine at position 139 (N139Q). Such a variant is shown in SEQ ID NO: 34. A preferred transmembrane protein portion for use in Exonuclease Sequencing comprises (a) a monomer comprising a variant
48/106 of SEQ ID NO: 4 having a methionine at position 113 (R113M), a cysteine at position 135 (L135C) and a glutamine at position 139 (N139Q) and (b) six monomers each comprising a variant of SEQ ID NO: 4 having a methionine at position 113 (R113M) and a glutamine at position 139 (N139Q). The six monomers in (b) each preferably comprise the sequence shown in SEQ ID NO: 34. The variant may be a naturally occurring variant that is naturally expressed by an organism, for example by a Staphilococcus bacterium.
Alternatively, the variant can be expressed in vitro or recombinantly by bacteria such as Escherichia coli.
Variants also include non-naturally occurring variants produced by recombinant technology.
Over the entire length of the amino acid sequence of SEQ ID NO: 4, a variant will preferably be at least 50% homologous to this sequence based on the amino acid identity.
More preferably, the variant polypeptide can be at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90% and more preferably at least 95%, 97% or 99% homologous based on the amino acid identity with the amino acid sequence of SEQ ID NO: 4 in the entire sequence.
It can have at least 80%, for example at least 85%, 90% or 95%, of amino acid identity in relation to a stretch of 200 or more, for example 230, 250, 270 or 280 or more, contiguous amino acids (“ difficult homology ”). Homology can be determined as discussed above.
Amino acid substitutions can be made to the amino acid sequence of SEQ ID NO: 4 in addition to those discussed above, for example up to 1, 2, 3, 4, 5, 10, 20 or 30 substitutions.
Conservative substitutions can be made as discussed above.
One or more amino acid residues from the amino acid sequence of SEQ ID NO: 4 can be additionally deleted from the
49/106 polypeptides described above.
Up to 1, 2, 3, 4, 5, 10, 20 or 30 residues can be deleted, or more.
The variants can be fragments of SEQ ID NO: 4. Such fragments retain the activity that forms pore.
The fragments can be at least 50, 100, 200 or 250 amino acids in length.
A fragment preferably comprises the pore-forming domain of SEQ ID NO: 4. Fragments typically include residues 119, 121, 135, 113 and 139 of SEQ ID NO: 4. One or more amino acids can be alternatively or additionally added to the polypeptides described above.
An extension can be provided at the amino or carboxy terminal of the amino acid sequence of SEQ ID NO: 4 or a variant or fragment thereof.
The length can be very short, for example 1 to 10 amino acids in length.
Alternatively, the extension can be longer, for example up to 50 or 100 amino acids.
A carrier protein can be fused to a subunit or variant.
One or more amino acids can be alternatively or additionally added to the polypeptides described above.
An extension can be provided at the amino or carboxy terminal of the amino acid sequence of SEQ ID NO: 4 or a variant or fragment thereof.
The length can be very short, for example 1 to 10 amino acids in length.
Alternatively, the extension can be longer, for example up to 50 or 100 amino acids.
A carrier protein can be fused to a pore or variant.
As discussed above, a variant of SEQ ID NO: 4 is a subunit that has an amino acid sequence that varies from that of SEQ ID NO: 4 and that retains its ability to form a pore.
A variant typically contains the regions of SEQ ID NO: 4 that are responsible for pore formation.
The pore-forming ability of α-HL, which contains
50/106 a β tube, is provided by the β filaments in each subunit.
A variant of SEQ ID NO: 4 typically comprises the regions in SEQ ID NO: 4 that form β filaments.
The amino acids of SEQ ID NO: 4 that form β filaments are discussed above.
One or more modifications can be made to the regions of SEQ ID NO: 4 which form β filaments as long as the resulting variant retains its ability to form a pore.
The specific modifications that can be made to the β filament regions of SEQ ID NO: 4 are discussed above.
A variant of SEQ ID NO: 4 preferably includes one or more modifications, such as substitutions, additions or deletions, within its α helices and / or loop regions.
The amino acids that form α helices and loops are discussed above.
The variant can be modified to assist in its identification or purification as discussed above.
A particularly preferred pore for use in Exonuclease Sequencing comprises a subunit shown in SEQ ID NO: 36 (ie, α-HL-E287C-QC-D5FLAGH6) and six subunits shown in SEQ ID NO: 34 (ie, α -HL-Q). Pores derived from α-HL can be manufactured as discussed above with reference to pores derived from Msp.
In some embodiments, the transmembrane protein pore is chemically modified.
The pore can be chemically modified in any way and anywhere.
The transmembrane protein pore is preferably chemically modified by the attachment of a molecule to one or more cysteines (cysteine attachment), the attachment of a molecule to one or more lysines, the attachment of a molecule to one or more unnatural amino acids, enzymatic modification of an epitope or modification of a terminal.
Suitable methods for making such modifications are well known in the art.
The protein pore of
51/106 transmembrane can be chemically modified by binding any molecule.
For example, the pore can be chemically modified by binding a dye or a fluorophore.
Any number of monomers in the pore can be chemically modified.
One or more, such as 2, 3, 4, 5, 6, 7, 8, 9 or 10, of the monomers are preferably chemically modified as discussed above.
In some embodiments, the transmembrane protein pore comprises a molecular adapter that facilitates the detection of the analyte.
The pores for use in Exonuclease Sequencing typically comprise a molecular adapter.
The molecular adapter can directly facilitate the detection of the analyte by mediating an interaction between the pore and the analyte.
In such embodiments, the presence of the adapter improves the guest host chemistry of the pore and analyte and thereby improves the pore's ability to detect the analyte.
The principles of guest-host chemistry are well known in the art.
The adapter has an effect on the physical or chemical properties of the pore that improves its interaction with the analyte.
The adapter can alter the load of the pore tube or channel or specifically interacts with or binds to the analyte thereby facilitating its interaction with the pore.
In other embodiments, the molecular adapter indirectly facilitates the detection of the analyte by mediating an interaction between the pore and a product, such as a fragment, formed from the processing of the analyte.
For example, for Exonuclease Sequencing, the molecular adapter facilitates an interaction between the pore and individual digested nucleotides of the polynucleotide analyte.
In such embodiments, the presence of the adapter improves the guest host chemistry of the pore and the individual nucleotides and thus
52/106 improves the ability of the pore to detect individual nucleotides.
The adapter has an effect on the physical or chemical properties of the pore that improve its interaction with the individual nucleotides.
The adapter can alter the load of the pore tube or channel or specifically interact with or bind to the individual nucleotides thereby facilitating their interaction with the pore.
The molecular adapter is preferably a cyclic molecule such as a cyclodextrin, a species that is capable of hybridization, a DNA ligand or interquel, a peptide or peptide analog, a synthetic polymer, an aromatic planar molecule, a positively charged small molecule or a small molecule capable of binding hydrogen.
The adapter can be cyclic.
A cyclic adapter preferably has the same symmetry as the pore.
The adapter preferably has eight-fold symmetry if the pore is derived from Msp since Msp typically has eight subunits around a central axis.
The adapter preferably has seven times symmetry if the pore is derived from α-HL whereas α-HL typically has seven subunits around a central axis.
This is discussed in more detail below.
The adapter typically interacts with the analyte through the chemistry of the host host.
The adapter is typically capable of interacting with a nucleotide or polynucleotide.
The adapter comprises one or more chemical groups that are capable of interacting with the analyte, such as the nucleotide or polynucleotide.
The one or more chemical groups preferably interact with the analyte, nucleotide or polynucleotide by non-covalent interactions, such as hydrophobic, hydrogen bonding, Van der Waal forces, π cation interactions and / or electrostatic forces.
The one or more chemical groups that are capable of interacting with the nucleotide or polynucleotide are preferably positively charged.
The one or more chemical groups that are able to interact with
The nucleotide or polynucleotide most preferably comprises amino groups.
The amino groups can be attached to the primary, secondary or tertiary carbon atoms.
The adapter even more preferably comprises a ring of amino groups, such as a ring of 6, 7 or 8 amino groups.
The adapter most preferably comprises a ring of seven or eight amino groups.
A ring of protonated amino groups can interact with negatively charged phosphate groups on the nucleotide or polynucleotide.
The correct positioning of the adapter within the pore can be facilitated by the chemistry of the host host between the adapter and the pore.
The adapter preferably comprises one or more chemical groups that are capable of interacting with one or more amino acids in the pore.
The adapter most preferably comprises one or more chemical groups that are capable of interacting with one or more amino acids in the pore through non-covalent interactions, such as hydrophobic, hydrogen bonding, Van der Waal forces, π and cation interactions / or electrostatic forces.
Chemical groups that are able to interact with one or more amino acids in the pore are typically hydroxyls or amines.
Hydroxyl groups can be attached to primary, secondary or tertiary carbon atoms.
Hydroxyl groups can form hydrogen bonds with uncharged amino acids in the pore.
Any adapter that facilitates the interaction between the pore and the nucleotide or polynucleotide can be used.
Suitable adapters include, but are not limited to, cyclodextrins, cyclic peptides and cucurbiturils.
The adapter is preferably a cyclodextrin or a derivative thereof.
The cyclodextrin or derivative thereof can be any of those disclosed in Eliseev, A.
V., and Schneider, H-J. (1994) J.
Am.
Chem.
Soc. 116, 6081-6088. The adapter is most preferably heptacis-6-amino-β-cyclodextrin (am7-βCD), 6-monodeoxy-6-monoamino-β-cyclodextrin (am1- βCD) or heptacis- (6-deoxy-6-guanidine) -cyclodextrin (gu7-βCD). The group
54/106 guanidine in gu7-βCD has a much higher pKa than the primary amines in am7-βCD and thus more positively charged. this gu7-βCD adapter can be used to increase the residence time of the nucleotide in the pore, to increase the accuracy of the measured residual current, as well as to increase the base detection rate at high temperatures or low data acquisition rates.
If a succinimidyl 3- (2-pyridyldithio) propionate (SPDP) crosslinker is used as discussed in more detail below, the adapter is preferably heptacis (6-deoxy-6-amino) -6-N-mono (2-pyridyl ) dithiopropanoyl-β-cyclodextrin (am6amPDP1-βCD). The most suitable adapters include γ-cyclodextrins, which comprise 8 sugar units (and therefore have eight-fold symmetry). The γ-cyclodextrin can contain a binding molecule or can be modified to comprise all or more of the modified sugar units used in the examples of β-cyclodextrin discussed above.
The molecular adapter is preferably covalently attached to the pore.
The adapter can be covalently attached to the pore using any method known in the art.
The adapter is typically connected via the chemical connection.
If the molecular adapter is linked via cysteine binding, one or more cysteines were preferably introduced into the mutant by substitution.
As discussed above, Msp-derived monomers can comprise a cysteine residue in one or more of positions 88, 90, 91, 103 and 105. Each monomer in the pore can be chemically modified by attaching a molecular adapter to one or more, such as 2, 3, 4 or 5, of these cysteines.
Alternatively, the monomer can be chemically modified by attaching a molecule to one or more cysteines introduced in other positions.
The molecular adapter is preferably attached to one or more of positions 90, 91 and 103 of SEQ ID NO: 2.
55/106
For α-HL derived pores, the correct orientation of the adapter within the pore tube or channel and the covalent connection of the adapter to the pore can be facilitated using specific pore modifications.
In particular, each pore subunit preferably has glutamine at position 139 of SEQ ID NO: 2. One or more of the pore subunits may have an arginine at position 113 of SEQ ID NO: 2. One or more of the pore subunits may have a cysteine in position 119, 121 or 135 of SEQ ID NO: 2 to facilitate the attachment of the molecular adapter to the pore.
The reactivity of cysteine residues can be enhanced by modifying adjacent residues.
For example, the basic groups of flanking residues of arginine, histidine or lysine will change the pKa of the cysteines of the thiol group to those of the more reactive S- group.
The reactivity of cysteine residues can be protected by thiol protective groups such as dTNB.
These can be reacted with one or more pore cysteine residues before a ligand is attached.
The molecule (with which the pore is chemically modified) can be linked directly to the pore or linked via a linker as disclosed in International Order Nos.
PCT / GB09 / 001690 (published as WO 2010/004273), PCT / GB09 / 001679 (published as WO 2010/004265) or PCT / GB10 / 000133 (published as WO 2010/086603). In a preferred embodiment, the detector comprises a protein that binds polynucleotide.
This allows the method of the invention to be used to sequence polynucleotides or nucleic acids.
Polynucleotides are defined below.
Examples of proteins that bind polynucleotides include, but are not limited to, enzymes that treat nucleic acid, such as nucleases, polymerases, topoisomerases, ligases and helicases, and not catalytically binding proteins such as those classified by the SCOP (Structural Classification of Proteins ) under the superfamily of the protein that binds nucleic acid (50249). The protein binding
56/106 polynucleotide is preferably modified to remove and / or replace cysteine residues as described in International Application No.
PCT / GB10 / 000133 (published as WO 2010/086603). A preferred polynucleotide binding protein is derived from Phi29 polymerase.
The protein preferably comprises the sequence shown in SEQ ID NO: 6 or a variant thereof.
This is discussed in more detail below.
Other preferred polynucleotide-binding proteins for use in the invention include E. coli exonuclease I (SEQ ID NO: 8), E. coli exonuclease III enzyme (SEQ ID NO: 10), T. thermophilus RecJ (SEQ ID NO: 12) and lambda bacteriophage exonuclease (SEQ ID NO: 14) and variants thereof.
Three identical subunits of SEQ ID NO: 14 interact to form a trimester exonuclease.
The variant is preferably modified to facilitate binding to the membrane protein and can be any of those discussed in International Application No.
PCT / GB09 / 001679 (published as WO 2010/004265) or PCT / GB10 / 000133 (published as WO 2010/086603). The protein can be any of SEQ ID NOs: 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46 , 48 and 50 described in International Order No.
PCT / GB10 / 000133 (published as WO 2010/086603) or a variant thereof discussed in this International Application.
The polynucleotide binding protein can be attached to the pore in any way and is preferably attached as described in International Application No.
PCT / GB09 / 001679 (published as WO 2010/004265) or PCT / GB10 / 000133 (published as WO 2010/086603). The detector preferably comprises a protein that binds polynucleotide in addition to a pore of transmembrane protein.
Such detectors form modular sequencing systems that can be used in the sequencing methods of the invention.
The polynucleotide-binding protein may be bound to the pore, but it is not required to be.
In Exonuclease Sequencing, the target polynucleotide is
57/106 allowed to interact with an exonuclease present in the detector.
The exonuclease is typically attached to the pore in the detector.
In Filament Sequencing, the detector typically comprises a polymerase in addition to the pore.
The target polynucleotide is allowed to interact with the polymerase, such as Phi29 polymerase, present in the detector.
The polymerase and the pore are typically not bonded together, but together form the detector.
For Exonuclease Sequencing, the exonuclease is preferably covalently linked to the transmembrane protein pore.
The exonuclease can be covalently attached to the pore using any method known in the art.
The pore and protein can be chemically fused or genetically fused.
The pore and exonuclease are genetically fused if the entire construct is expressed from a single polynucleotide sequence.
The genetic fusion of a pore to an exonuclease is discussed in International Order No.
PCT / GB09 / 001679 (published as WO 2010/004265). If the exonuclease is attached to the pore via cysteine binding, one or more cysteines have preferably been introduced into the pore by substitution.
The pores derived from Msp can naturally comprise cysteine residues in one or more of the positions 10 to 15, 51 to 60, 136 to 139 and 168 to 172. These positions are present in the loop regions that have low conservation between counterparts indicating that mutations or insertions can be tolerated.
They are therefore suitable for binding an exonuclease.
The reactivity of the cysteine residues can be enhanced by the modification as described above.
The exonuclease can be linked directly to the pore or via one or more ligands.
The exonuclease can be attached to the pore using the hybridization ligands described in International Application No.
PCT / GB10 / 000132 (published as WO 2010/086602). Alternatively, peptide linkers can be used.
Peptide ligands are sequences of
58/106 amino acid.
The length, flexibility and hydrophilicity of the peptide ligand are typically designed so that it does not disturb pore functions and exonuclease.
Preferred flexible peptide linkers are stretches 2 to 20, such as 4, 6, 8, 10 or 16, serine and / or glycine amino acids.
More preferred flexible binders include (SG) 1, (SG) 2, (SG) 3, (SG) 4, (SG) 5 and (SG) 8 where S is serine and G is glycine.
Preferred rigid linkers are stretches 2 to 30, such as 4, 6, 8, 16 or 24, proline amino acids.
Most preferred rigid binders include (P) 12 where P is proline.
The detector may comprise a pore of transmembrane protein chemically modified with a molecular adapter and an exonuclease.
Such detectors are useful for Exonuclease Sequencing.
For Exonuclease Sequencing, the most preferred detector comprises (a) a pore derived from α-HL, (b) an exonuclease covalently attached to the pore and (c) a cyclodextrin or a derivative thereof.
In this preferred embodiment, the pore preferably comprises a subunit shown in SEQ ID NO: 36 (i.e., α-HL- E287C-QC-D5FLAGH6) and six subunits shown in SEQ ID NO: 34 (i.e., α-HL -Q). The exonuclease is preferably E. coli exonuclease I (SEQ ID NO: 8) or a variant thereof.
The cyclodextrin derivative is preferably heptacis-6-amino-β-cyclodextrin (am7-βCD), 6-monodeoxy-6-monoamino-β-cyclodextrin (am1-βCD) or heptacis- (6-deoxy-6-guanidine) - cyclodextrin (gu7-βCD). For filament sequencing, a preferred detector comprises (a) a pore derived from Msp and (b) a Phi29 polymerase.
The pore and polymerase are not bonded together.
This preferred embodiment is discussed in more detail below.
The detector can be present as an individual or single detector.
Alternatively, the detector may be present in a population
59/106 homologous or heterologous to two or more detectors.
Polynucleotide A polynucleotide, such as a nucleic acid, is a macromolecule that comprises two or more nucleotides.
The polynucleotide or nucleic acid bound by the protein can comprise any combination of any nucleotide.
Nucleotides can be naturally occurring or artificial.
The nucleotide can be oxidized or methylated.
One or more nucleotides in the polynucleotide can be damaged.
For example, the polynucleotide can comprise a pyrimidine dimer.
Such dimers are typically associated with damage by ultraviolet light and are the primary cause of skin melanomas.
A nucleotide typically contains a nucleobase, a sugar and at least one phosphate group.
The nucleobase is typically heterocyclic.
Nucleobases include, but are not limited to, purines and pyrimidines and more specifically adenine, guanine, thymine, uracil and cytosine.
Sugar is typically a pentose sugar.
Nucleotide sugars include, but are not limited to, ribose and deoxyribose.
The nucleotide is typically a ribonucleotide or deoxyribonucleotide.
The nucleotide typically contains a monophosphate, diphosphate or triphosphate.
The phosphates can be linked on the 5 'or 3' side of a nucleotide.
Nucleotides include, but are not limited to, adenosine monophosphate (AMP), adenosine diphosphate (ADP), adenosine triphosphate (ATP), guanosine monophosphate (GMP), guanosine diphosphate (GDP), guanosine triphosphate (GTP) ), thymidine monophosphate (TMP), thymidine diphosphate (TDP), thymidine triphosphate (TTP), uridine monophosphate (UMP), uridine diphosphate (UDP), uridine triphosphate (UTP), cytidine monophosphate (CMP) , cytidine diphosphate (CDP), cytidine triphosphate (CTP), cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), deoxyadenosine monophosphate (dAMP),
60/106 deoxyadenosine diphosphate (dADP), deoxyadenosine triphosphate (dATP), deoxyguanosine monophosphate (dGMP), deoxyguanosine diphosphate (dGDP), deoxyguanosine triphosphate (dGTP), deoxyphine phosphate ), deoxythymidine triphosphate (dTTP), deoxyuridine monophosphate (dUMP), deoxyuridine diphosphate (dUDP), deoxyuridine triphosphate (dUTP), deoxycidine monophosphate (dCMP), deoxycycline (dCMP) detoxify . The nucleotides are preferably selected from AMP, TMP, GMP, CMP, UMP, dAMP, dTMP, dGMP or dCMP.
A nucleotide can contain a sugar and at least one phosphate group (that is, it lacks a nucleobase). The nucleotides in the polynucleotide can be linked together in any way.
Nucleotides are typically linked by sugar and phosphate groups as in nucleic acids.
Nucleotides can be connected via their nucleobases as in pyrimidine dimers.
The polynucleotide can be single-stranded or double-stranded.
At least a portion of the polynucleotide is preferably double-stranded.
A single-stranded polynucleotide may have one or more primers hybridized to it and therefore comprise one or more short regions of double-stranded polynucleotide.
The primers can be of the same type of polynucleotide as the target polynucleotide or it can be a different type of polynucleotide.
The polynucleotide can be a nucleic acid, such as deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). The polynucleotide can be any synthetic nucleic acid known in the art, such as peptide nucleic acid (PNA), glycerol nucleic acid (GNA), threose nucleic acid (TNA), locked nucleic acid (LNA) or other synthetic polymers with chains nucleotide sides.
The polynucleotide bound by
The protein is preferably single stranded, such as cDNA, RNA, GNA, TNA or LNA.
The protein-bound polynucleotide is preferably double-stranded, such as DNA.
Proteins that bind single-stranded polynucleotides can be used to sequence double-stranded DNA as long as the double-stranded DNA is dissociated into a single strand before it is bound by the protein.
If the Filament Sequencing method of the invention is used the polynucleotide analyte typically contains a portion that is double stranded although in general only one strand is sequenced.
In a standard primer / configuration, the standard filament is typically sequenced (i.e., 5 'passing through the pore). In any case, for strand sequencing, a double stranded polynucleotide preferably comprises a single strand leader sequence.
The leader sequence can be of any length, but is typically 27 to 150 nucleotides in length, such as 50 to 150 nucleotides in length.
The addition of single-stranded polynucleotide sections to a double-stranded polynucleotide can be accomplished in several ways.
A chemical or enzymatic bond can be made.
In addition, the Nextera method by Epicenter is suitable.
A PCR method was developed using a sense primer which, as usual, contains a complementary section for the beginning of the target region of genomic DNA, but was additionally preceded with a 50 polyT section.
To prevent polymerase from extending the complementary filament opposite the polyT section and thereby creating an abrupt end PCR product (as is normal), four abasic sites have been added between the polyT section and the complementary priming section.
These abasic sites will prevent the polymerase from extending beyond this region and thus the polyT section will remain as 5 'single-stranded DNA in each of the amplified copies.
62/106
Absorption by the nanopore If the detector comprises a pore, the method of the invention preferably further comprises letting the analyte interact with the detector and measuring the current that passes through the pore during the interaction and thereby determining the presence or absence or characteristics of the analyte.
The analyte is present if the current flows through the pore in a manner specific to the analyte (that is, if a distinctive current associated with the analyte is detected flowing through the pore). The analyte is absent if the current does not flow through the pore in a specific way for the analyte.
Similarly, the characteristics of the analyte can be determined using the current that flows through the pore during the interaction.
The invention therefore involves the absorption by the nanopore of an analyte.
The invention can be used to differentiate analytes of similar structure based on the different effects they have on the current that passes through the pore.
The invention can also be used to measure the concentration of a particular analyte in a sample.
The invention can also be used in a sensor that uses many or thousands of pores in mass absorption applications.
The method can be carried out using any suitable membrane system (such as an amphiphilic layer or a lipid bilayer) in which a pore is inserted into a membrane.
The method is typically performed using (i) an artificial membrane (such as an amphiphilic layer or a lipid bilayer) comprising a pore, (ii) an isolated, naturally occurring lipid bilayer comprising a pore, or (iii) a cell having a pore inserted into it.
The method is preferably carried out using an artificial membrane (such as an amphiphilic layer or a lipid bilayer). The membrane can comprise other transmembrane and / or intramembrane proteins as well as other molecules in addition to the pore.
The appliance and the appropriate conditions
63/106 are discussed below with reference to the sequencing embodiments of the invention.
The method of the invention is typically carried out in vitro.
During the interaction between the analyte and the pore, the analyte affects the current that flows through the pore in a specific way for that analyte.
For example, a particular analyte will reduce the current flowing through the pore for a particular average period of time and to a particular degree.
In other words, the current that flows through the pore is distinctive for a particular analyte.
Control experiments can be performed to determine the effect that a particular analyte has on the current flowing through the pore.
The results of carrying out the method of the invention on a test sample can then be compared with those derived from such a control experiment in order to identify a particular analyte in the sample, determine whether a particular analyte is present in the sample or determine the characteristics of the analyte.
The frequency at which the current flowing through the pore is affected in a manner indicative of a particular analyte can be used to determine the concentration of that analyte in the sample.
Polynucleotide sequencing methods The present invention also provides methods of estimating the sequence of an analyte that is a target polynucleotide.
The present invention also provides methods for sequencing an analyte that is a target polynucleotide.
A polynucleotide is a macromolecule that comprises two or more nucleotides.
The nucleotides can be any of those discussed above, including methylated, oxidized and damaged nucleotides.
The polynucleotide can be any of those discussed above and is preferably a nucleic acid.
These methods are possible because the pore of transmembrane proteins can be used to differentiate nucleotides in structure
64/106 similar based on the different effects they have on the current that passes through the pore.
Individual nucleotides can be identified at the level of a single molecule from their current amplitude when they interact with the pore.
The nucleotide is present in the pore (individually or as part of a polynucleotide) if the current flows through the pore in a manner specific to the nucleotide (that is, if a distinctive current associated with the nucleotide is detected flowing through the pore). Successive identification of nucleotides in a target polynucleotide allows the sequence of the polynucleotide to be determined.
In one embodiment, the method comprises (a) attaching the target polynucleotide to a membrane; (b) letting the target polynucleotide interact with a detector present in the membrane, wherein the detector comprises a transmembrane pore and an exonuclease, so that the exonuclease digests an individual nucleotide at one end of the target polynucleotide; (c) letting the nucleotide interact with the pore; (d) measuring the current that passes through the pore during the interaction and thereby determining the identity of the nucleotide; and (e) repeating steps (b) to (d) at the same end of the target polynucleotide and thereby determining the sequence of the target polynucleotide.
In another embodiment, the method comprises (a) attaching the target polynucleotide to a membrane; (b) letting the target polynucleotide interact with a detector present in the membrane, where the detector comprises a pore of transmembrane protein, a molecular adapter that facilitates an interaction between the pore and one or more nucleotides and an exonuclease, so that the exonuclease digests an individual nucleotide at one end of the target polynucleotide; (c) letting the nucleotide interact with the adapter; (d) measuring the current that passes through the pore during the interaction and thereby determining the identity of the nucleotide; and (e) repeat steps (b) to (d) at the same end of the target polynucleotide and thereby determine the
65/106 sequence of the target polynucleotide.
Consequently, the method involves the absorption by the nanopore of a proportion of the nucleotides in a target polynucleotide in a successive manner in order to sequence the target polynucleotide.
The individual nucleotides are described above and below.
This is Exonuclease Sequencing.
In another embodiment, the method comprises: (a) attaching the target polynucleotide to a membrane; (b) letting the target polynucleotide interact with a detector present in the membrane, wherein the detector comprises a transmembrane pore, so that the target polynucleotide moves through the pore; and (c) measuring the current that passes through the pore as the target polynucleotide moves with respect to the pore and thereby determining the sequence of the target polynucleotide.
In another embodiment, the method comprises (a) attaching the target polynucleotide to a membrane; (b) letting the target polynucleotide interact with a detector present in the membrane, where the detector comprises a pore of transmembrane protein and a protein that binds polynucleotide, preferably a polymerase, so that the protein controls the movement of the target polynucleotide through the pore and a proportion of the nucleotides in the target polynucleotide interact with the pore; and (c) measuring the current passing through the pore during each interaction and thereby determining the sequence of the target polynucleotide.
Consequently, the method involves the absorption by the nanopore of a proportion of the nucleotides in a target polynucleotide as the individual nucleotides pass through the tube or channel in order to sequence the target polynucleotide.
This is the Filament Sequencing.
These methods of the invention are particularly adapted for the sequencing of target polynucleotides, such as nucleic acids, because the binding of the nucleic acid sequences to the membrane decreases by several orders of magnitude the amount of polynucleotide required.
At
66/106 concentrations at which target polynucleotides can be sequenced using the invention are discussed above.
The whole or only part of the target polynucleotide can be sequenced using this method.
The polynucleotide can be of any length.
For example, the polynucleotide can be at least 10, at least 50, at least 100, at least 150, at least 200, at least 250, at least 300, at least 400 or at least 500 nucleotides in length.
The polynucleotide can be 1000 or more nucleotides or 5000 or more nucleotides in length.
The polynucleotide can be naturally occurring or artificial.
For example, the method can be used to check the sequence of a manufactured oligonucleotide.
The methods are typically performed in vitro.
Nucleotides (digested from the target polynucleotide or present in the polynucleotide) can interact with the pore on each side of the membrane.
Nucleotides can interact with the pore in any way and anywhere.
As discussed above, the nucleotides preferably reversibly bind to the pore via or in conjunction with the adapter.
The nucleotides most preferably reversibly bind to the pore via or in conjunction with the adapter as they pass through the pore through the membrane.
The nucleotides can also reversibly attach to the pore tube or channel via or in conjunction with the adapter as they pass through the pore through the membrane.
During the interaction between a nucleotide and the pore, the nucleotide affects the current that flows through the pore in a manner specific to that nucleotide.
For example, a particular nucleotide will reduce the current flowing through the pore for a particular average period of time and to a particular degree.
In other words, the current that flows through the pore is distinctive for a particular nucleotide.
The experiments
67/106 controls can be performed to determine the effect that a particular nucleotide has on the current flowing through the pore.
The results of performing the method of the invention on a test sample can then be compared with those derived from such a control experiment in order to determine the sequence of the target polynucleotide.
Sequencing methods can be performed using any suitable membrane / pore system in which a pore is present in or inserted into a membrane.
The methods are typically performed using a membrane comprising naturally occurring or synthetic lipids.
The membrane is typically formed in vitro.
The methods are preferably not performed using an isolated, naturally occurring membrane comprising a pore, or a cell expressing a pore.
The methods are preferably carried out using an artificial membrane.
The membrane can comprise other transmembrane and / or intramembrane proteins as well as other molecules in addition to the pore.
The membrane forms a barrier to the flow of ions, nucleotides and polynucleotides.
The membrane is preferably an amphiphilic layer such as a lipid bilayer.
Lipid bilayers suitable for use according to the invention are described above.
The sequencing methods of the invention are typically performed in vitro.
Sequencing methods can be performed using any apparatus that is suitable for investigating a membrane / pore system in which a pore is present in or inserted within a membrane.
The method can be carried out using any device that is suitable for absorption by the nanopore.
For example, the apparatus comprises a chamber comprising an aqueous solution and a barrier which separates the chamber into two sections.
The barrier has an opening in which the membrane containing the pore is formed.
The analyte can be linked to
68/106 membrane in each of the two sections of the chamber.
Sequencing methods can be performed using the apparatus described in International Order No.
PCT / GB08 / 000562. The methods of the invention involve measuring the current that passes through the pore during interaction with the nucleotide or as the target polynucleotide moves with respect to the pore.
Therefore, the device also comprises an electrical circuit capable of applying a potential and measuring an electrical signal through the membrane and pore.
The methods can be performed using a patch-clamp or a voltage clamp.
The methods preferably involve the use of a voltage clamp.
The sequencing methods of the invention involve measuring a current that passes through the pore during interaction with the nucleotide or as the target polynucleotide moves with respect to the pore.
Suitable conditions for measuring ionic currents through the transmembrane protein pores are known in the art and disclosed in the Example.
The method is typically carried out with a voltage applied across the membrane and pore.
The voltage used is typically from -400 mV to +400 mV.
The voltage used is preferably in a range having a selected lower limit of -400 mV, -300 mV, -200 mV, -150 mV, - 100 mV, -50 mV, -20 mV and 0 mV and an upper limit independently selected from +10 mV, +20 mV, +50 mV, +100 mV, +150 mV, +200 mV, +300 mV and +400 mV.
The voltage used is most preferably in the range of 100 mV to 240 mV and most preferably in the range of 160 mV to 240 mV.
It is possible to increase the discrimination between different nucleotides by a pore by using an increased applied potential.
Sequencing methods are typically performed in the presence of any alkali metal chloride salt.
In the exemplary apparatus discussed above, salt is present in the aqueous solution in the chamber.
Potassium chloride (KCl), sodium chloride (NaCl) or cesium chloride (CsCl) are
69/106 typically used.
KCl is preferred.
The salt concentration is typically 0.1 to 2.5 M, 0.3 to 1.9 M, 0.5 to 1.8 M, 0.7 to 1.7 M, 0.9 at 1.6 M or from 1 M to 1.4 M.
The salt concentration is preferably 150 mM to 1 M.
High salt concentrations provide a high signal-to-noise ratio and allow currents indicative of the presence of a nucleotide to be identified against the background of normal current fluctuations.
The lowest salt concentrations can be used if nucleotide detection is carried out in the presence of an enzyme, such as when sequencing polynucleotides.
This is discussed in more detail below.
The methods are typically performed in the presence of a buffer.
In the exemplary apparatus discussed above, the buffer is present in the aqueous solution in the chamber.
Any buffer can be used in the method of the invention.
A suitable buffer is Tris-HCl buffer.
The methods are typically performed at a pH of 4.0 to 12.0, 4.5 to 10.0, 5.0 to 9.0, 5.5 to 8.8, 6.0 to 8 , 7 or 7.0 to 8.8 or 7.5 to 8.5. The pH used is preferably about 7.5. The methods are typically carried out from 0 ° C to 100 ° C, from 15 ° C to 95 ° C, from 16 ° C to 90 ° C, from 17 ° C to 85 ° C, from 18 ° C to 80 ° C, from 19 ° C to 70 ° C, or from 20 ° C to 60 ° C.
The methods can be performed at room temperature.
The methods are preferably carried out at a temperature that supports the enzyme function, such as about 37 ° C.
As mentioned above, good nucleotide discrimination can be achieved at low salt concentrations if the temperature is increased.
In addition to increasing the temperature of the solution, there are several other strategies that can be used to increase the conductance of the solution, while maintaining conditions that are suitable for the activity of the enzyme.
One such strategy is to use the lipid bilayer to divide two different concentrations of saline, a low salt concentration of salt on the enzyme side and a higher concentration on the opposite side.
a
70/106 example of this method is to use 200 mM KCl on the cis side of the membrane and 500 mM KCl in the trans chamber.
Under these conditions, conductance through the pore is expected to be approximately equivalent to 400 mM KCl under normal conditions, and the enzyme will only experience 200 mM if placed on the cis side.
Another possible benefit of using asymmetric saline conditions is the osmotic gradient induced through the pore.
This liquid flow of water can be used to push nucleotides into the pore for detection.
A similar effect can be achieved using a neutral osmolyte, such as sucrose, glycerol or PEG.
Another possibility is to use a solution with relatively low levels of KCl and rely on a species that carries an additional charge that is less able to disrupt the enzyme's activity.
The target polynucleotide that is analyzed can be combined with known protective chemistries to protect the polynucleotide from acting on the binding protein or exonuclease while in the bulky solution.
The pore can then be used to remove the protective chemistry.
This can be achieved by using protective groups that are not hybridized by the pore, binding protein or enzyme under an applied potential (WO 2008/124107) or by using the protective chemicals that are removed by the binding protein or enzyme when maintained in immediate proximity to the pore (J Am Chem Soc. 22 Dec 2010; 132 (50): 17961-72). Exonuclease Sequencing In one embodiment, the method of sequencing an analyte that is a target polynucleotide involves letting the target polynucleotide interact with an exonuclease enzyme.
Any of the exonuclease enzymes discussed above can be used in the method.
The exonuclease releases individual nucleotides from one end of the target polynucleotide.
The enzyme can be covalently attached to the pore as discussed above.
An individual nucleotide is a single nucleotide.
An individual nucleotide is one that is not linked to another nucleotide or
71/106 polynucleotide by a nucleotide bond.
A nucleotide bond involves one of the phosphate groups of one nucleotide being attached to the sugar group of another nucleotide.
An individual nucleotide is typically one that is not linked by a nucleotide bond to another polynucleotide of at least 5, at least 10, at least 20, at least 50, at least 100, at least 200, at least 500, at least 1000 or at least 5000 nucleotides.
For example, the individual nucleotide was digested from a target polynucleotide, such as a strand of DNA or RNA.
The individual nucleotide can be any of those discussed above.
Exonucleases are enzymes that typically cling to one end of a polynucleotide and digest the polynucleotide one nucleotide at a time from that end.
The exonuclease can digest the polynucleotide in the 5 'to 3' direction or in the 3 'to 5' direction. The end of the polynucleotide to which the exonuclease binds is typically determined by choosing the enzyme used and / or using methods known in the art.
Hydroxyl groups or hood structures at each end of the polynucleotide can typically be used to prevent or facilitate binding of the exonuclease to a particular end of the polynucleotide.
The method involves letting the polynucleotide interact with the exonuclease so that the nucleotides are digested from the end of the polynucleotide at a rate that allows the identification of a proportion of nucleotides as discussed above.
Methods for doing this are well known in the art.
For example, Edman degradation is used to successively digest unique amino acids from the polypeptide end so that they can be identified using High Performance Liquid Chromatography (HPLC). A homologous method can be used in the present invention.
The rate at which the exonuclease works is typically slower than the ideal rate for a wild-type exonuclease.
A fee
72/106 Proper exonuclease activity in the sequencing method involves digestion from 0.5 to 1000 nucleotides per second, from 0.6 to 500 nucleotides per second, from 0.7 to 200 nucleotides per second, from 0.8 to 100 nucleotides per second, from 0.9 to 50 nucleotides per second or from 1 to 20 or 10 nucleotides per second.
The rate is preferably 1, 10, 100, 500 or 1000 nucleotides per second.
An adequate rate of exonuclease activity can be achieved in several ways.
For example, variant exonucleases with an ideally reduced rate of activity can be used according to the invention.
The Exonuclease Sequencing methods of the invention have additional advantages in addition to reducing the amount of polynucleotide required.
The presentation of single-stranded DNA in solution to an exonuclease-Nano-pore (“X-Pore”) / membrane system under potential was studied.
When the DNA analyte is introduced into the system, the pore can become blocked permanently or temporarily, preventing the detection of individual nucleotides.
When one end of the DNA analyte is located away from the pore, for example by binding to the membrane, it has surprisingly been found that this blockage is no longer observed.
It also increases the number of potential DNA passage events for the enzyme due to the increased effective concentration of being on the same plane as the analyte.
This acts to decrease the binding time between the analytes and increases the sequencing throughput.
Filament Sequencing Filament Sequencing involves the controlled and staggered displacement of polynucleotides through a pore.
A polynucleotide is a macromolecule that comprises two or more nucleotides.
The protein-bound polynucleotide can comprise any combination of any nucleotide.
The nucleotides can be any of those discussed above.
The invention's Filament Sequencing method typically uses a protein that binds polynucleotide to control the movement of the target polynucleotide through the pore. Examples of such proteins are given above. The polynucleotide binding protein is preferably a polynucleotide treating enzyme. A polynucleotide treatment enzyme is a polypeptide that is able to interact with and modify at least one property of a polynucleotide. The enzyme can modify the polynucleotide by cleaving it to form individual nucleotides or shorter nucleotide chains, such as di- or trinucleotides. The enzyme can modify the polynucleotide by orienting it or moving it to a specific position. The polynucleotide treatment enzyme does not need to demonstrate enzymatic activity as long as it is able to bind the target polynucleotide and control its movement through the pore. For example, the enzyme can be modified to remove its enzyme activity or it can be used under conditions that prevent it from acting as an enzyme. Such conditions are discussed in more detail below. The polynucleotide treatment enzyme is preferably derived from a nucleolytic enzyme. The polynucleotide treatment enzyme used in the construction of the enzyme is most preferably derived from a member of any of the Enzyme Classification (EC) groups 3.1.11, 3.1.13, 3.1.14, 3.1.15, 3.1.16, 3.1.21, 3.1.22, 3.1.25,
3.1.26, 3.1.27, 3.1.30 and 3.1.31. The enzyme can be any of those disclosed in International Application No. PCT / GB10 / 000133 (published as WO 2010/086603). Preferred enzymes are polymerases, exonucleases, helicases, translocases and topoisomerases, such as gyrases. Suitable enzymes include, but are not limited to, E. coli exonuclease I (SEQ ID NO: 8), E. coli exonuclease III enzyme (SEQ ID NO: 10), T. RecJ
74/106 thermophilus (SEQ ID NO: 12) and bacteriophage lambda exonuclease (SEQ ID NO: 14) and variants thereof.
Three subunits that comprise the sequence shown in SEQ ID NO: 14 or a variant of the same interact to form a trimeric exonuclease.
The enzyme is most preferably derived from the Phi29 DNA polymerase.
An enzyme derivative of Phi29 polymerase comprises the sequence shown in SEQ ID NO: 6 or a variant thereof.
According to one embodiment, the polynucleotide binding protein is bound or bound to the membrane and is capable of both binding to the analyte polynucleotide and then controlling the displacement of the analyte through the pore.
In this embodiment, the analyte polynucleotide can be attached to the membrane via the polynucleotide binding protein.
The analyte polynucleotide and the polynucleotide binding protein can both be bound to the membrane, preferably by different binding methods.
The polynucleotide binding protein is preferably a helicase.
A variant of SEQ ID NOs: 6, 8, 10, 12 or 14 is an enzyme that has an amino acid sequence that varies from that of SEQ ID NOs: 6, 8, 10, 12 or 14 and that retains the binding capacity of polynucleotide.
The variant may include modifications that facilitate the binding of the polynucleotide and / or facilitate its activity at high salt concentrations and / or at room temperature.
Over the entire length of the amino acid sequence of SEQ ID NO: 6, 8, 10, 12 or 14, a variant will preferably be at least 50% homologous to this sequence based on the amino acid identity.
More preferably, the variant polypeptide can be at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90% and more preferably at least 95%, 97% or 99% homologous based on the identity of
75/106 amino acid with the amino acid sequence of SEQ ID NO: 6, 8, 10, 12 or 14 in the entire sequence.
It can have at least 80%, for example at least 85%, 90% or 95%, of amino acid identity in relation to a stretch of 200 or more, for example 230, 250, 270 or 280 or more, contiguous amino acids (“ difficult homology ”). Homology is determined as described above.
The variant may differ from the wild-type sequence in any of the modes discussed above with reference to SEQ ID NO: 2. The enzyme can be covalently attached to the pore as discussed above.
The enzyme is not required to be as close to the pore lumen as for individual nucleotide sequencing as there is no potential to disrupt the series in which the nucleotides reach the pore absorption portion.
The two strategies for filament DNA sequencing are the displacement of DNA through the nanopore, both from cis to trans and from trans to cis, with or against an applied potential.
One of the most advantageous mechanisms for Filament Sequencing is the controlled displacement of single-stranded DNA through the nanopore under an applied potential.
Exonucleases that act progressively or processively on double-stranded DNA can be used on the cis side of the pore to feed the remaining single strand through under an applied potential or on the trans side under a reverse potential.
Likewise, a helicase that unwinds the double-stranded DNA can also be used in a similar way.
There are also possibilities for sequencing applications that require filament displacement against an applied potential, but the DNA must first be "captured" by the enzyme under a reverse potential or none.
With the potential then switched back to what follows the filament bond it will move from cis to trans through the pore and will be kept in a conformation prolonged by the current flow.
Exonucleases of single-stranded DNA or
76/106 single-stranded DNA-dependent polymerases can act as molecular motors to push the newly translocated single strand back through the pore in a scaled-down, trans-to-cis way against the applied potential.
Alternatively, single-stranded DNA-dependent polymerases can act as a molecular brake that slows down the movement of a polynucleotide through the pore.
In most preferred embodiments, Filament Sequencing is performed using a pore derived from Msp and a Phi29 DNA polymerase.
The method may comprise (a) attaching the target polynucleotide to a membrane; (b) letting the target polynucleotide interact with a membrane detector, which comprises a pore derived from Msp and a Phi29 DNA polymerase, so that the polymerase controls the movement of the target polynucleotide through the pore; and (c) measure the current that passes through the pore as the target polynucleotide moves with respect to the pore and thereby determine the sequence of the target polynucleotide, in which steps (b) and (c) are carried out with a voltage applied across the pore.
The method may comprise (a) attaching the target polynucleotide to a membrane; (b) letting the target polynucleotide interact with a membrane detector, which comprises a pore derived from Msp and a Phi29 DNA polymerase, so that the polymerase controls the movement of the target polynucleotide through the pore and a proportion of the nucleotides in the polynucleotide target interacts with the pore; and (c) measuring the current passing through the pore during each interaction and thereby determining the sequence of the target polynucleotide, in which steps (b) and (c) are carried out with a voltage applied through the pore.
When the target polynucleotide is contacted with a Phi29 DNA polymerase and a pore derived from Msp, the target polynucleotide first forms a complex with the Phi29 DNA polymerase.
When the voltage is applied through the pore,
77/106 the target polynucleotide / Phi29 DNA polymerase complex forms a complex with the pore and controls the movement of the target polynucleotide through the pore.
These Msp / Phi29 embodiments have three unexpected advantages.
First, the target polynucleotide moves through the pore at a rate that is commercially viable while allowing for efficient sequencing.
The target polynucleotide moves through the Msp pore more quickly than it does through a hemolysin pore.
Second, an increased current range is observed as the polynucleotide moves through the pore, letting the sequence be more easily determined.
Third, a decreased current variation is observed when the specific pore and polymerase are used together thereby increasing the signal-to-noise ratio.
Any polynucleotide described above can be sequenced.
At least a portion of the polynucleotide is preferably double-stranded.
The pore can be any of the pores discussed above.
The pore can comprise eight monomers comprising the sequence shown in SEQ ID NO: 2 or a variant thereof.
Phi29 wild-type DNA polymerase has polymerase and exonuclease activity.
It can also unpack double-stranded polynucleotides under the right conditions.
Consequently, the enzyme can function in three ways.
This is discussed in more detail below.
The Phi29 DNA polymerase can comprise the sequence shown in SEQ ID NO: 6 or a variant thereof.
A variant of SEQ ID NO: 6 is an enzyme that has an amino acid sequence that varies from that of SEQ ID NO: 6 and that retains polynucleotide binding activity.
The variant must work in at least one of the three modes
78/106 discussed below.
Preferably, the variant works in all three modes. the variant may include modifications that facilitate the treatment of the polynucleotide and / or facilitate its activity at high salt concentrations and / or at room temperature.
Over the entire length of the amino acid sequence of SEQ ID NO: 6, a variant will preferably be at least 40% homologous to that sequence based on the amino acid identity.
More preferably, the variant polypeptide can be at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90% and more preferably at least 95%, 97% or 99% homologous based on the amino acid identity to the amino acid sequence of SEQ ID NO: 4 in the entire sequence.
It can have at least 80%, for example at least 85%, 90% or 95%, of amino acid identity in relation to a stretch of 200 or more, for example 230, 250, 270 or 280 or more, contiguous amino acids (“ difficult homology ”). Homology is determined as described above.
The variant may differ from the wild-type sequence in any of the modes discussed above with reference to SEQ ID NO: 2. The enzyme can be covalently attached to the pore as discussed above.
Any of the systems, apparatus or conditions discussed above can be used in accordance with this preferred embodiment.
The salt concentration is typically 0.15 M to 0.6 M.
The salt is preferably KCl.
The method can be carried out in one of three preferred modes based on the three modes of Phi29 DNA polymerase.
Each mode includes a method of checking the sequence.
First, the method is preferably carried out using Phi29 DNA polymerase as a polymerase.
In this embodiment, steps (b) and (c) are performed in the presence of free nucleotides and an enzyme cofactor so that the polymerase moves the polynucleotide
79/106 target through the pore against the field resulting from the applied voltage.
The target polynucleotide moves from 5 'to 3'. The free nucleotides can be one or more of any of the individual nucleotides discussed above.
The enzyme cofactor is a factor that allows Phi29 DNA polymerase to function as a polymerase or an exonuclease.
The enzyme cofactor is preferably a divalent metal cation.
The divalent metal cation is preferably Mg2 +, Mn2 +, Ca2 + or Co2 +. The enzyme cofactor is most preferably Mg2 +. The method preferably further comprises (d) removing the free nucleotides so that the polymerase moves the target polynucleotide through the pore with the field resulting from the applied voltage (i.e., in the 3 'and 5' direction) and a proportion of the nucleotides in the target polynucleotide interacts with the pore and (e) measure the current that passes through the pore during each interaction and thus check the sequence of the target polynucleotide obtained in step (c), where steps (d) and (e) are also carried out with a voltage applied through the pore.
Second, the method is preferably carried out using Phi29 DNA polymerase as an exonuclease.
In this embodiment, in which steps (b) and (c) are carried out in the absence of free nucleotides and the presence of an enzyme cofactor so that the polymerase moves the target polynucleotide through the pore with the field resulting from the voltage applied.
The target polynucleotide moves from 3 'to 5'. The method preferably further comprises (d) adding free nucleotides so that the polymerase moves the target polynucleotide through the pore against the field that results from the applied voltage (i.e., in the 5 'to 3' direction) and a proportion of the nucleotides in the target polynucleotide interacts with the pore and (e) measure the current that passes through the pore during each interaction and thus check the sequence of the target polynucleotide obtained in step (c), in which steps (d) and (e) are also carried out with a voltage applied through the pore.
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Third, the method is preferably carried out using Phi29 DNA polymerase in the decompression mode.
In this embodiment, steps (b) and (c) are carried out in the absence of free nucleotides and the absence of an enzyme cofactor so that the polymerase controls the movement of the target polynucleotide through the pore with the field that results from the voltage applied (since it is unzipped). In this embodiment, the polymerase acts as a brake preventing the target polynucleotide from moving through the pore very quickly under the influence of the applied voltage.
The method preferably further comprises (d) decreasing the voltage applied through the pore so that the target polynucleotide moves through the pore in the opposite direction to that in steps (b) and (c) (that is, as it anneals) and a proportion of the nucleotides in the target polynucleotide interact with the pore and (e) measure the current that passes through the pore during each interaction and thus check the sequence of the target polynucleotide obtained in step (c), in which steps (d) and (e) are also carried out with a voltage applied through the pore.
Kits The present invention also provides kits for sequencing an analyte that is a target polynucleotide.
The kit comprises (a) a transmembrane pore, such as a transmembrane protein pore, (b) a protein that binds polynucleotide and (c) means for attaching the target polynucleotide to a membrane.
In a preferred embodiment, the polynucleotide binding protein is an exonuclease and the kit further comprises a molecular adapter that facilitates an interaction between the pore and one or more nucleotides in the target polynucleotide.
Such a kit can be used for Exonuclease Sequencing.
In another preferred embodiment, the kit comprises components of a membrane, such as the phospholipids needed to form a lipid bilayer.
The means for attaching the target polynucleotide to a membrane
81/106 preferably comprise a reactive group.
Suitable groups include, but are not limited to, thiol, cholesterol, lipid and biotin groups.
Any of the embodiments discussed above with reference to the methods of the invention are equally applicable to the kits of the invention.
The kits of the invention may additionally comprise one or more other reagents or instruments that enable any of the above-mentioned embodiments to be performed.
Such reagents or instruments include one or more of the following: suitable buffer (s) (aqueous solutions), means for obtaining a sample from an individual (such as a vessel or an instrument comprising a needle), means for amplify and / or express polynucleotides, a membrane as defined above or voltage or contact clamping apparatus.
The reagents can be present in the kit in a dry state so that a fluid sample resuspends the reagents.
The kit can also optionally comprise instructions to enable the kit to be used in the method of the invention or details referring to which of the patients the method can be used.
The kit can optionally comprise nucleotides.
Apparatus The invention also provides an apparatus for sequencing an analyte that is a target polynucleotide.
The apparatus comprises (a) a membrane, (b) a plurality of transmembrane pores in the membrane, (c) a plurality of proteins that bind polynucleotides and (d) a plurality of target polynucleotides bound to the membrane.
The plurality of proteins that bind polynucleotide can be on the membrane.
The apparatus may be any conventional analyte analysis apparatus, such as an array or a chip.
In a preferred embodiment, the polynucleotide binding protein is an exonuclease and the apparatus comprises a molecular adapter that facilitates
82/106 an interaction between the pore and one or more nucleotides in the target polynucleotide. Such an apparatus can be used for Exonuclease Sequencing. Any of the embodiments discussed above with reference to the methods of the invention are equally applicable to the kits of the invention. The apparatus preferably comprises: a sensor device that is capable of supporting the membrane and the plurality of pores and is operable to perform polynucleotide sequencing using the pores and proteins; and at least one reservoir to contain the material to perform the sequencing. The apparatus preferably comprises: a sensor device that is capable of supporting the membrane and the plurality of pores and is operable to perform polynucleotide sequencing using the pores and proteins; at least one reservoir to contain material to perform the sequencing; a fluidic system configured to controllably supply material from at least one reservoir to the sensor device; and one or more, such as a plurality, of containers for receiving the respective samples, the fluidic system being configured to supply the samples selectively from the one or more containers for the sensor device. The apparatus can be any of those described in International Application No. PCT / GB08 / 004127 (published as WO 2009/077734), PCT / GB10 / 000789 (published as WO 2010/122293), International Application No. PCT / GB10 / 002206 (not yet published) or International Application No. PCT / US99 / 25679 (published as WO 00/28312). The Examples that follow illustrate the invention:
1. Example 1 - Exonuclease sequencing
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1.1 Materials and Methods
1.1.1 Materials and Oligonucleotides Oligonucleotides were purchased from ADTBio or IDTDNA. Details of the exact sequences and modifications can be found in the Table below (SEQ ID NOs 18 to 21). Modification Comp. SEQ Name Code String 5 'Internal 3' (nt) ID NO: Forn.
TTTTTTTTTTTTTTTTTTTTTTTTTT ONLA ATDBio Chol-TEG - - 70 TTTTTTTTTTTTTTTTTTTTTTTTTTTT 18 0692 A8691 TTTTTTTTTTTTTTTTTTT
AAAAAAAAAAAAAAAAAAAAAA ONLA AAAAAAAAAAAAAAAAAAAAAA ATDBio Chol-TEG - - 70 19 0682 AAAAAAAAAAAAAAAAAAAAAA A887 YYYY
CCCCCCCCCCCCCCCCCCCCCCCCCC ONLA ATDBio Chol-TEG - - 70 CCCCCCCCCCCCCCCCCCCCCCCC 20 0683 A8874 CCCCCCCCCCCCCCCCCCCCCCCC
TTTTTTTTTTTTTTTTTTTTTTTTTT ONLA Estrep- IDT - - 70 TTTTTTTTTTTTTTTTTTTTTTTTTTTT 18 0693 Btn: ssDNA 60739014 TTTTTTTTTTTTTTTTTTT
TGTGTTCTATGTCTTATTCTTACTT ONLA Estrep- IDT - - 70 CGTTATTCTTGTCTCTATTCTGTTT 21 0694 Btn: ssDNA 60739013 ATGTTTCTTGTTTGTTAGCA TTTTTTTTTTTTTTTTTTTTTTTTTTT
ONLA IDT - - - 70 TTTTTTTTTTTTTTTTTTTTTTTTTTT 18 0706 60692267
TTTTTTTTTTTTTTTTTTT Recombinant Streptavidin, expressed in E. coli, was purchased from Sigma Aldrich (S0677). The synthetic lipids 1,2-difitanoil-sn-glycero-3-phosphocholine (16: 0 4ME PC) and 1,2-dipalmitoyl-sn-glycero-3 phosphoethanolamine-N-cap biotinyl (16: 0 Cap Biotinila PE) were purchased from Avanti Polar Lipids.
1.1.2 HPLC Purification of Mono-Substituted Streptavidin 1 μM of DNA modified with 5'-biotin was mixed with μM of streptavidin in 25 mM Tris.HCl, 400 mM KCl, 10 mM MgCl2, pH 7.5 and incubated for 30 min at 22 ° C. Estrep conjugates: mono-substituted DNA were separated using an Agilent 1200 analytical LC system comprising a binary pump, column oven maintained at 23 ° C, UV detector with 13 μl flow cell, with both the sample compartment and fractions maintained at 4 ° C. The column was an Agilent BioMonolith QA conducted at 1 ml min-1, and the samples were separated into a gradient of 30 mM - 1.1 M NaCl in 100 mM Tris pH 8.5. Quantification of mono-substituted Estrep: DNA conjugates
Purified 84/106 was performed using densitometry following gel electrophoresis using a series of DNA patterns to create a standard curve.
1.1.3 Single Channel Records of Planar Lipid Bilayer The bilayers were formed by the apposition of two monolayers of 100% 16: 0 4ME PC or 95% 16: 0 4ME PC, 5% 16: 0 Cap Biotinila PE. The bilayers were formed through an opening of 60 to 150 μm in diameter in Teflon film (25 μm in thickness from Goodfellow, Malvern, PA), which divided a chamber into two buffer compartments (cis and trans) each with a volume of 1 ml. The bilayers were formed through the opening by consecutively raising the buffer level in each compartment until a high-strength seal was observed (≥10 GΩ). Unless otherwise stated, DNA and protein were added to the cis compartment, which was connected to the bottom. No reagents were added to the trans compartment, which was connected to the tip stage of the amplifier. Unless otherwise stated, experiments were performed in 25 mM Tris.HCl, 400 mM KCl, 10 mM MgCl2, pH 7.5, at 22 ° C.
1.2 Results
1.2.1 Detection of Single Molecule of Tied Analytes The detection rates of nanopore for free single-stranded DNA in solution can be determined by measuring the number of DNA translocations (events) through the nanopore per second. A DNA shift can be identified by a transient signature current block in the digital record. For tied analytes the number of interactions can similarly be calculated as long as the DNA is only transiently tied to the bilayer, such as via a cholesterol group. As the free end of the DNA enters the nanopore it will reside in the tube until the tied end becomes free of the bilayer and thus the molecule can translocate (Fig. 2A and 2B). If the mooring
85/106 is more stable so the block will be permanent (Fig. 2C and 2D). A mixture of 50% PolyA and PoliC modified with cholesterol (ONLA0682 and ONLA0683 respectively) were tested at 10, 100 and 1000 pM final concentration to establish the effect of Col-DNA on the event rate and residence time (Table below) . This was compared to the event rate for free single stranded DNA.
Free analyte Tied analyte 100 nM 10 pM 100 pM 1000 pM 120 mV rate 0.01 0.015 0.045 2.5 Event 160 mV 0.74 0.15 1.05 26
The rates of increase with voltage at all concentrations (Table above) and of course the event rates are higher at higher concentrations.
At lower concentrations and voltages the event rates are too low to actually be considered significant.
That is, most, if not all, events in these conditions are likely to be only the occasional false positive.
It is somewhat surprising, however, that at higher current levels a significant number of DNA events are observed with only 10 pM of DNA.
Despite the DNA concentration that is at least 100 times lower, the event rates are much higher with cholesterol-modified DNA.
It is somewhat surprising that at the highest current levels (≥ 160 mV) a significant number of DNA events are still observed with only 10 pM of DNA and these DNA events occur at a frequency similar to 100 nM of unmodified ssDNA.
DNA tying can be estimated to improve DNA analyte detection by 3 to 4 orders of magnitude.
For certain applications the transitory nature of the mooring would be preferred.
If a stable mooring molecule were attached directly to the 5 'or 3' ends of the DNA then some sequence data would be lost since the sequencing round could not continue to the end of the DNA, due to the distance between the bilayer and the site of
86/106 active enzymes. If the binding is more transient then when the tied end randomly becomes free of the bilayer then the enzyme can process the DNA until completion.
1.3 Conclusions The potential to improve the detection efficiency of a nanopore detector for an analyte by approximately 3 to 4 orders of magnitude has been demonstrated here. Rapid pore blockage suggests that this tied analyte is still available for proteins in both the solution and the bilayer (such as an enzyme or nanopore construction respectively) and thus has the potential as a mechanism for releasing the pore itself or a construct of nanopore-enzyme. Several means of binding analyte to the lipid bilayer are available and most have been reported in relation to ssDNA binding, since functional chemistry can be easily incorporated during oligonucleotide synthesis. In the preferred medium a biotin-modified ddNTP can be incorporated into the 3 'end of ssDNA using terminal transferase. By mixing with streptavidin the DNA of the analyte can then be added to a single pore in a lipid bilayer that contains 1 to% Biotin PE where it will be tied. Alternatively if the sequence is known then the DNA can be hybridized to the complementary synthetic DNA already modified at one end to be lipophilic. Another advantage of tying the analyte is that you have control over one end of the DNA. It can be seen above that DNA will quickly block the pore if one end is kept in close proximity, in the above case it is the bilayer. If a DNA treatment enzyme, such as an exonuclease, is attached to the nanopore then it will bind to one end of the DNA and again locate it in the pore and thus the other end will quickly block. If the DNA is immobilized however then when the enzyme binds to one end
87/106 so both are now occupied and unavailable to the pore. The need for an analyte requirement under DNA sequencing is for applications such as single cell sequencing for epigenetics and also screening low volume biological samples. The current Illumina Genome analyzer system requires 100 ng to 1 μg of DNA for a prep library. sequencing. A single 128-channel chip for nanopore sequencing would use ~ 0.5 ng of DNA without the need for amplification; based on the 1000mer fragment generation and reading length at a concentration of 10 pM.
2. Example 2 - Filament Sequencing In addition to the work to bind ssDNA to the lipid membrane for Exonuclease Sequencing, the technique can also be adapted to a Filament Sequencing method. In Filament Sequencing, a portion of a polynucleotide filament is tied through the nanopore under an applied potential. The strand is typically DNA or RNA, for example single-stranded or double-stranded DNA. Preferably the strand is single-stranded DNA (ssDNA). The base residues included in the filament interact with the nanopore and a signal is generated that is characteristic of each residue. The filament is moved through the pore, causing variation to the signal. The signal can be used to infer the sequence of the DNA strand. One embodiment of Filament Sequencing uses a pore of protein embedded in a lipid membrane. Electrodes are placed on each side of the lipid membrane in an electrolyte and a potential is applied through the system. Under the potential, the polynucleotide moves to the pore. The current through the protein pore can be measured and used to recognize bases as they pass through the pore's transmembrane tube. Typically the protein pore will be a bacterial membrane protein, such as a porin or a toxin. Preferably the
88/106 pore is a hemolysin, a gramicidin or an MspA.
The rate at which DNA travels through a pore can be very fast to allow accurate identification of each base, so it may be desirable to slow the speed of displacement.
One method to slow down the displacement of a DNA strand is to use a DNA treatment protein, such as a DNA polymerase.
The DNA treatment protein can be attached to the pore, for example by covalent bonding, directly or via linker groups.
Typically the DNA treatment protein is bound to the pore for Exonuclease Sequencing applications.
Usually, for the sequencing of filament applications, the DNA treatment protein is not bound to the pore.
For a Filament Sequencing method, it is desirable to have a DNA treatment protein that has a very long binding time at the top of the nanopore.
A long binding time allows many nucleotides to be processed through the DNA treatment protein and thus through the nanopore.
For a polymerase, a typical processing rate can be around 20 nucleotides per second.
A bonding time of 10 minutes would allow movement of 12,000 nucleotides.
A binding time of one minute would allow 120 nucleotides to be processed.
Using this method, a long connection time is also related to the reading length.
Currently, a reading length of around 100 nucleotides would be sufficient for existing rival technologies, although longer reading lengths are desirable, for example a reading length of 200, 500 or 1000 nucleotides.
Preferred reading lengths are at least 5000 nucleotides, more preferably 10,000 or 50,000 nucleotides.
An advantage of a long reading length is that it greatly reduces the complexity of the bioinformatics needed to analyze
89/106 sequencing. Typically a DNA treatment protein is a DNA polymerase. Preferred DNA treatment proteins include Phi29 DNA polymerase.
2.1 Materials and Methods The bilayers were formed by the apposition of two monolayers of 100% DPhPC or 99% DPhPC, 1% 16: 0 Cap Biotinila PE. The bilayers were formed through an opening of 60 to 150 μm in diameter in Teflon film (25 μm in thickness from Goodfellow, Malvern, PA), which divided a chamber into two buffer compartments (cis and trans) each with a volume of 1 ml. The bilayers were formed through the opening by consecutively increasing the level of buffer in each compartment until a high resistance seal was observed (≥10 GΩ). Unless otherwise stated, DNA and protein were added to the cis compartment, which was connected to the earth. No reagents were added to the trans compartment, which was connected to the tip stage of the amplifier. The experiments were carried out with 400 mM KCl, 25 mM Tris.HCl, 10 μM EDTA, pH 7.5. The hemolysin mutant used was HL- (E111N / K147N) 7 (SEQ ID NO: 38). 1 μM of 5'-biotin-modified DNA (StrandDNA1) was mixed with 10 μM of streptavidin in 25 mM Tris.HCl, 400 mM KCl, 10 mM MgCl2, pH 7.5 and incubated for 30 min at 22 ° Ç. Estrep conjugates: mono-substituted DNA were separated using an Agilent 1200 analytical LC system comprising a binary pump, column oven maintained at 23 ° C, UV detector with 13 μl flow cell, with both the sample compartment and fractions kept at 4 ° C. The column was an Agilent BioMonolith QA conducted in 1 ml min-1, and the samples were separated in a gradient of 30 mM - 1.1 M NaCl in 100 mM Tris pH 8.5. Quantification of Estrep: DNA conjugates
Purified 90/106 mono-substituted was performed using densitometry following gel electrophoresis using a series of DNA patterns to create a standard curve.
To form StrandDNA3, the DNA-streptavidin complex was hybridized with a 5x excess of StrandDNA2 by heating at 50 ° C for 10 minutes in a PCR heating block.
The temperature was reduced to 23 ° C at a rate of 2 degrees per minute.
For the rounds of membrane mooring, the bilayer was formed with 99% DPhPC, 1% 16: 0Cap Biotinila PE.
Once the bilayer was formed, 1 nM of StrandDNA3 was added to the cis chamber and mixed well.
A control section was recorded for 5 minutes at +180 mV to obtain DNA binding events to the nanopore.
After the control section was recorded, 5 nM KF (negative exo) (NEB) was added and the signal was recorded for 5 minutes at +180 mV.
For runs where the analyte is in solution, the bilayer was formed with 100% DPhPC.
StrandDNA6 was produced by the hybridization of StrandDNA4 and StrandDNA5 in equimolar concentrations.
Hybridization was performed by heating to 50 ° C in a PCR block for 10 minutes, after cooling to 23ºC at 2ºC / min.
Once the bilayer is formed, 400 nM of StrandDNA6 was added to the cis chamber and mixed well.
A control section was recorded for 5 minutes at +180 mV to obtain DNA binding events to the nanopore.
After the control section was recorded, 800 nM KF (negative exo) (NEB) was added and the signal was recorded for 5 minutes at +180 mV.
The open pore level was visually estimated, and the DNA displacement events were defined to be occasions when the data fell below a threshold placed at about 5 sigmas below the pore level (where sigma is the noise standard deviation). Any obvious artifacts were manually removed from the data before the event was detected.
The average current level of each event is shown in the figures
91/106 in pA (vertical axis) vs the event duration in seconds (horizontal axis). Note that the horizontal axis is demonstrated using a logarithmic scale, as the event duration ranges from less than a millisecond to as much as 10 seconds. In all four cases there were also numerous very short events (less than 1 ms) that were excluded. This is because they are too short for their current levels to be reliably estimated, and because they are not meant to distinguish between the different conditions shown. StrandDNA1: 5’-Biotin-TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT
TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTGGCTACGACCTGC ATGAGAATGC-3 '(SEQ ID NO: 22) StrandDNA2: 5'-CTCACCTATCCTTCCACTCACCCCCCAAAAAACCCC CCAAAAAACCCCCCAAAAAAGCATTCTCATGCAGGTCGTAGCC-3' (SEQ ID NO: 23) StrandDNA3: StrandDNA1 hybridized to StrandDNA2 (SEQ ID NO's: 22 and 23) StrandDNA4: 5'-AACCCCCAAAAACCCCCAAAAACCCCCAAAAACCC
CCAAAAACCCCCAAAAACCCCCAAAAACCCCCAAAAACCCCCATA GAGACAAGAATAACGAAGTA-3 ’(SEQ ID NO: 24) StrandDNA5: 5’-TACTTCGTTATTCTTGTCTCTAT-3 (SEQ ID NO: 25) StrandDNA6: StrandDNA6: StrandD4: StrandD4: StrandD4
2.2 Results An experiment was developed that allows a DNA treatment protein to be evaluated for its ability to hold onto DNA under the application of a potential. In this experiment, a DNA enzyme complex is pulled into the nanopore resulting in a characteristic current level. When the DNA enzyme complex dissociates, the DNA is pulled deeper into the nanopore
92/106 resulting in a second current level.
The DNA then completely travels through the nanopore, resulting in an open pore and resetting the system to its original state.
The kinetics of DNA-enzyme binding can be assessed by examining the duration of the enzyme-bound state during multiple repetitions of this process (Fig. 3). In recent work, a polymerase was used to control the displacement of a DNA strand.
To run such an experiment, the DNA concentration is ideally from 100 to 1000 nM to be captured by the nanopore.
As the enzyme binds to DNA, it is preferable for the enzyme concentration to be at a molarity similar to DNA, or in excess of DNA.
It is common for the enzyme concentrations to be used to double the DNA concentration to ensure that a large (preferably all) proportion of the DNA forms an enzyme-DNA complex.
This places a high demand on the amount of material required.
It is therefore desirable to have a system that uses less DNA and therefore less enzyme.
One method of achieving this is to tie the DNA to the lipid membrane.
As shown, the DNA insertion rate can be greatly increased by enhancing the interaction between DNA and membrane.
This can produce rates that are comparable to those when the DNA is free in solution, but using 1,000 to 10,000 times less material.
By using a lower concentration of DNA, the concentration of enzyme used can be greatly reduced (see Fig. 4). A suitable DNA treatment protein is the Klenow Fragment (KF) (N. THE.
Wilson, R.
Abu-Schmays, B.
Gyarfas, H.
Wang, K. R.
Lieberman, M.
Akeson and W. B.
Dunbar (2009). Electronic Control of DNA Polymerase Binding and Unbinding to Single DNA Molecules.
ACS Nano 3, 995-1003). The Klenow fragment is a large protein fragment produced when E. coli DNA polymerase I is enzymatically cleaved
93/106 by the subtilisin protease. It retains the 5'-3 'polymerase activity and the 3' → 5 'exonuclease activity for removal of pre-encoded and read-proof nucleotides, but loses its 5' → 3 'exonuclease activity. KF can also be genetically engineered to remove the remaining 3 ’→ 5’ exonuclease activity. This DNA treatment protein typically binds to DNA at the interface between single-stranded and double-stranded DNA (standard primer / junction) and can catalyze the replication of the DNA strand by adding nucleotides. The Klenow fragment was investigated for the Filament Sequencing methods but was found to have binding times of 1 to 100 ms when pulled at the top of a nanopore by applying a potential. KF was screened in an analyte configuration tied to the membrane as shown above (Fig. 4). When the DNA is in solution, the binding time of the KF-DNA complex is from 1 to 100 ms (Fig. 5 and 6) (similar to the published results (ref Wilson / Akeson 2009)). This is too short to be useful for a Filament Sequencing method since a 100 ms duration would only allow a few nucleotides to be read. However, when the DNA is tied to the lipid membrane, the binding time increases to 0.1 to 10 s (Figs. 7 and 8).
2.3 Conclusions The duration of the enzyme-DNA complex at the top of the pore is a function of the strength of the applied field that acts on the loaded DNA strand. The protein's ability to resist this force determines how long the complex remains intact at the top of the pore. The longer residence time for stranded DNA may be due to mobile lipid molecules that apply additional force to the filament in the pore as it diffuses through the lipid membrane. This force neutralizes the force applied by the applied field and the net force that the KF experiences is reduced. This configuration benefits from
94/106 advantages that a high field offers (for example, the higher the signal for noise, the faster the DNA capture), but still allows the DNA treatment protein to have a long binding time at the top of the pore. The mooring method offers another means to control the behavior of the enzyme at the top of the nanopore. There are many possibilities for exploring this concept. By varying the composition of the membrane, or changing a physical parameter, such as temperature, it would be possible to change the diffusion rate of the molecule tied to the lipid bilayer, and consequently, the strength that the DNA enzyme complex experiences in the nanopore. In the Exonuclease Sequencing embodiment, increasing the fluidity of the membrane can increase the availability of polynucleotide for the exonuclease. The fluidity of the membrane can be changed by adding agents such as cholesterol. In addition, the nature of the binding agent can be changed to control the diffusion rate of the tied analyte to produce a similar effect. It is likely that binding to a large species, such as a protein, would produce a slower diffusion rate compared to binding to a small molecule such as a lipid. It has been shown that the rate of enzyme when it is complexed with polynucleotide and pulled into the nanopore will be affected by the field applied through the nanopore. It is likely that the diffusional strength of the analyte binding will reduce the net force that the enzyme in the pore experiences. It was predicted that the rate of movement of the polymer can be controlled by combining the strength of an applied potential with the diffusional strength of the analyte binding. Another potential use of this effect is to control the speed of the filament through the pore without using a DNA-treating protein. The force applied by the applied potential can be matched by the diffusional force of the membrane.
3. Example 3 - More Filament Sequencing In a recent work, Phi29 DNA polymerase was used to
95/106 to control the displacement of a DNA strand through α-hemolysin (Akeson et al., 2010, J Am Chem Soc. December 22, 2010; 132 (50): 17961-
72.). Two modes of controlled movement of a DNA strand through a nanopore have been reported using Phi29 as a molecular motor, both methods rely on their action at the junction of double / single strand DNA in a 5 'projection duplex. The movement can occur by polymerizing the primer filament that is hybridized opposite the filament to be interrogated or by a decompression method where the primer filament is sequentially not hybridized from the filament to be interrogated to reveal more and more of the target sequence that it was previously duplex DNA.
3.1 Materials and Methods As shown for single-stranded DNA, the mooring portion can be varied to generate strands that demonstrate a transient interaction with the bilayer or a longer-lasting mooring, for example with biotin cholesterol: streptavidin respectively. For dsDNA analytes, it would be considered that duplex DNA analytes that demonstrate transient binding behavior would be more suitable for Filament sequencing as well as to allow the enzyme to completely decompress the analyte and clear the nanopore ready for the next. Complementary oligos (ONLA1346 and ONLA1347, 65 nt and 31 nt respectively) have been designated to contain in the target filament (ONLA1346) a cholesterol group on the 3 'and a polyC extension that contains a single A on the 5'. When hybridized these Oligos give a duplex DNA of 31 base pairs with a 5 'projection of 34 nt so that the target strand can be moved inward and captured by the 5' nanopore first. The decompression can then be tracked by observing the movement of the single A, at the bottom of polyC, through the reading tip of the nanopore. For
96/106 compared to unbound analytes an identical strand in sequence to the target strand was designated but lacked the cholesterol group (ONLA1049). Single-channel recordings were performed using an MspA-NNNRRK mutant pore (ONLP2726) in combination with Phi29 DNA polymerase. A single channel was obtained and the cis buffer perfused with 10 ml of fresh buffer (400 mM KCl, 10 mM HEPES pH 8.0) to minimize the chance of single channel insertion. After a 5-minute control section, DNA was added to 0.5 nM or 100 nM, for both tied and untied experiments, respectively. Several short duration events (~ 10 ms) have been observed after the addition of DNA which are proposed to be the duplex DNA that is captured by the nanopore and the primer that is removed from the pattern by the force of the pore. After 5 min Phi29 DNA polymerase was added to the cis chamber to give 10 nM or 200 nM, again respectively for the tied and untied experiments. Used oligonucleotides: ONLA1346
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCTATTCTGTTTAT GTTTCTTGTTTGTTAGCC-Col (SEQ ID NO: 26) ONLA1347 GGCTAACAAACAAGAAACATAAACAGAATAG (SEQ ID NO: 27) ONLA1049
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCTATTCTGTTTAT GTTTCTTGTTTGTTAGCC (SEQ ID NO: 28) PoliT-50mer_XXXX_Sense
TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTXX XXXGGTTGTTTCTGTTGGTGCTGATATTGC (SEQ ID NO: 29) PhiX 235bp Anti-ACCACTAACTAAC:
97/106 PhiX 400bp Antisense Col-GACCGCCTCCAAACAATTTAGACA (SEQ ID NO: 31) PhiX 822bp Antisense Col-GGCAATCTCTTTCTGATTGTCCAG (SEQ ID NO: 32)
3.2 Results After the addition of Phi29 DNA polymerase several events of long duration were observed in both experiments which are proposed to be complexes of DNA capture: protein. These events show a short residence time at a constant level before oscillating between states, which are considered to occur at the start of unpacking and A starting to move through the pore reading tip. An example of this is shown in Figs. 12 and 11 for both tied (Fig. 9) and non-tied (Fig. 10) experiments. The analysis of all decompression events for DNA events both tied and in solution shows a widely constitutive pattern for the number of states observed, the average vs residence time for each state and the average vs standard deviation for each one (Fig 11 for not tied and Fig. 12 for tied). The position of the cholesterol is not adjusted to be at 3 'of the target strand and can be varied to 5' of the pattern or initiator strand or within a hairpin. Due to the requirement for the enzyme to fit in 3 'of the primer strand, the junction between single and double stranded DNA is considered to be not a suitable site for tying, however this has not been demonstrated experimentally. Although the mooring method works well for synthetic filaments, where binding chemistry can be incorporated during chemical synthesis of the oligonucleotide, applying it to samples derived from genomic DNA is more challenging. A common technique for amplifying sections of genomic DNA is using the polymerase chain reaction. On here
98/106 using two synthetic oligonucleotide primers several copies of the same section of DNA can be generated, where for each copy 5 'of each strand in the duplex will be the synthetic oligo.
By using an antisense primer that has a 5 'cholesterol group each copy of the amplified target DNA will contain a cholesterol group to tie.
The only problem with the analyte generated by the PCR is that it is terminated abruptly or contains a single 3'-A projection, none of which is suitable for tying to a nanopore for Filament Sequencing.
The addition of single stranded DNA sections to 5 'of duplex DNA is not easily possible.
A chemical or enzymatic bond can be made but none is highly efficient and also requires additional downstream reactions and purification steps.
A PCR method was developed using a sense primer which, as usual, contained a complementary section for the start of the target region of the genomic DNA but was additionally continued with a Section 50 polyT.
To prevent the polymerase from extending the complementary filament opposite the polyT section, to create an abrupt-ended PCR product as normal, four abasic sites have been added between the polyT Section and the complementary primer section.
These abasic sites will prevent the polymerase from extending beyond this region and thus the polyT section will remain as single-stranded 5 'DNA in each of the amplified copies (Figs. 13 and 14). Although this PCR method is an efficient way to link the 5 'polyT leader section, other methods for incorporating the binding chemistry are possible however, such as using terminal transferase to add to the 3' or via T4 polynucleotide kinase and ATPγS to add a 5 'reactive thiol for chemical bonding.
However, this method allows the generation of analytes strung in a form suitable for Filament Sequencing where the only limitation in size, and as such the reading length, is that it imposes by PCR (~ 20 kb). Single channel recordings were performed as described
99/106 above but using these fragments of genomic DNA amplified in order to observe any decompression event (Figs. 15 and 16). Several decompression events have been observed that have progressed and have since come out of their own accord, thus suggesting complete decompression of the duplex DNA. In order to observe an acceptable event rate for DNA capture complexes: protein for Filament Sequencing from solution after 100 nM DNA and 200 nM Phi29 DNA polymerase are required. For the 800 base pair fragment this is equivalent to ~ 50 μg of dsDNA per experiment, assuming the chamber volume of 1 ml as used above. Using tied dsDNA analytes the same acceptable event rate can be satisfied and exceeded using 0.1 nM DNA and 10 nM Phi29 DNA polymerase. For the 800 base pair fragment this is equivalent to ~ 50 ng dsDNA per experiment, assuming the 1 ml chamber volume as used above.
4. Example 4 - Solid State Sequencing The advantages demonstrated above for tying a lipid membrane can also be extended to solid-state nanopore experiments. Nanopores can be produced in solid materials and used in a similar way to biological nanopores. Its use and manufacture have been well documented elsewhere (WO 00/79257; WO 00/78668; Dekker C, Nat Nanotechnol. April 2007; 2 (4): 209-15; and Schloss JA, et al., Nat Biotechnol.Oct 2008; 26 (10): 1146- 53). Nanopores in solid-state materials, such as silicon nitride, offer advantages over biological channels such as pores. Solid-state materials are much less fragile than lipid membranes. Nanopores in solid material can be formed in a factory and have a long shelf life, unlike membranes
100/106 biologicals that are often formed in situ.
Recent advances with solid state nanopores also allow very thin materials such as graphene to be used that have unique properties (Golovchenko J, et al., Nature. 2010 Sep 9; 467 (7312): 190-3; Drndić M, et al., Nano Lett. 11 August 2010; 10 (8): 2915-21; and Dekker C, et al., Nano Lett. 11 August 2010; 10 (8): 3163-7). Nanointervals in graphene have also been proposed (Postma, 2008, Rapid Sequencing of Individual DNA Molecules in Graphene Nanogaps). Another embodiment of membranes in the solid state is to use a tunneling current between two or more electrodes embedded in the nanopore.
As an analyte passes through the pore (triggered by a trans membrane potential), the analyte facilitates a tunneling current between the electrode.
This current can be used to detect the identity of the analyte (Schloss supra; US 7,253,434; and WO 2008/092760). An alternative method for nanopores is to use nano intervals in solid-state materials as sensors (Chen et al., Materials Today, 2010, 13 (11): 28-41). Solid-state nanopore experiments can benefit from the advantages described above for lipid membranes.
A key difference between the two types of membrane is that amphiphilic membranes are often naturally mobile, acting essentially as a two-dimensional fluid with lipid diffusion rates of ~ 10-8 cm s-1, while membranes in materials such as silicon nitride are solid.
While there may be advantages to attaching an analyte to a surface in a static manner, it is desirable for the analyte to be able to move across with a membrane so that multiple analyte molecules can interact with the detector.
There are several schemes that can be used to tie an analyte to a solid state membrane (Fig. 17). THE
101/106 The first method would be to rely on the natural interaction of the analyte with an unmodified membrane, such as Si3N4. However, this provides very little control over the rate of diffusion of the analyte over the surface.
It is therefore preferable to modify the surface, the analyte, or both the surface and the analyte to provide the desired interaction.
Methods for chemically modifying materials in the solid state are well known in the art.
Solid state nanopores have also been chemically modified, either by self-assembly in solution or by activating reactive species through the nanopore under an applied potential (WO 2009/020682). The first two schemes use a chemically modified membrane to produce a surface where the analyte can transiently interact with the layer (Fig. 17A, B). In the first scheme, the mooring of the analyte group embeds itself within the modified layer (Fig. 17A). A long chain alkane can be attached to the surface and a mooring group such as cholesterol or an alkane would be used.
The surface modification can be achieved by the use of a chlorohexadecyl-dimethylsilane (or similar) and the methods described in WO 2009/020682. In the second scheme, the mooring analyte is not embedded within the layer, but resides on the surface.
This can be achieved using hydrophobics as in the first scheme.
In addition, similar methods can also be considered where the bonding of the analyte to the surface is mediated by electrostatic, hydrogen bonding or Van der Waals interactions.
The third scheme is the most similar to the membranes used with protein nanopores.
In this embodiment, the solid state membrane is modified to support a lipid monolayer (Fig. 17C). This method has all the benefits of the examples presented above for the
102/106 lipid membrane lashing.
Mooring can be achieved using an anchor or cholesterol link, through lipid tip groups, or through a receptor on the membrane.
Methods for forming bilayers or monolayers on solid surfaces are well known in the art (Duran RS, et al., Langmuir. March 13, 2007; 23 (6): 2924-7; and Cremer PS, et al., Surface Science Reports 2006; 61: 429-444). When the surface is made hydrophobic, a lipid monolayer can be formed spontaneously from lipid vesicles in solution.
The surface can be made hydrophobic in several ways, including plasma treatments (such as CH4) or chemical methods, such as chlorosilane chemistry (WO 2009/020682), and gold-thiol binding (Duran supra; and Cremer supra). A fourth scheme for tying analytes to membranes is to use a solid state membrane as a support for a lipid bilayer (Fig. 17D). In this embodiment, the detector element is the nanoporous membrane in the solid state.
This method has all the benefits of the examples presented above for the binding of the lipid membrane.
If the surface is made hydrophilic, the lipid bilayers will self-assemble on the surface - an effect that is common for bilayers formed on glass surfaces (Cremer supra). For all of the above examples, the solid-state nanopore can be combined with a protein that binds polynucleotide to form the detector.
Example 5 This Example describes how helicase-controlled DNA movement was not observed for unbound DNA when exposed to an MspA nanopore embedded in a triblock copolymer.
The chip has 128 reservoirs with platinum electrodes and an opening of 30 μm with a common platinum electrode attached to the lid.
The monolayers were formed with a 50 mg / ml solution mixture of triblock copolymer (TBCP 6-33-6, OH-PMOXA-
103/106 (PEG binder) -PDMS- (PEG binder) -PMOXA-OH, Polymer Source Product ID: P3691B-MOXZDMSMOXZ) in oil. The nanopore (MS- (G75S / G77S / L88N / D90N / D91N / D93N / D118R / Q126R / D134R / E139K) 8) was then added to the chip in the buffer. The reagents were only added through the top of the chip (cis side) once the chip was formed. The experiment was carried out with 625 mM sodium chloride, mM potassium ferricyanide, 75 mM potassium ferrocyanide, 100 mM HEPES, pH 8.0 (buffer 1). The MspA mutant used was MS- (G75S / G77S / L88N / D90N / D91N / D93N / D118R / Q126R / D134R / E139K) 8. The DNA sequence used in this experiment was a double-stranded 400mer strand (SEQ ID NO: 39 shows the sense strand sequence). SEQ ID NO: 39 - TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTG GTTGTTTCTGTTGGTGCTGATATTGCGCTCCACTAAAGGGCCGATT GACCCGGTGGTACCTTGGTTGTTTCTGTTGGTGCTGATATTGCTTTT GATGCCGACCCTAAATTTTTTGCCTGTTTGGTTCGCTTTGAGTCTTC TTCGGTTCCGACTACCCTCCCGACTGCCTATGATGTTTATCCTTTGG ATGGTCGCCATGATGGTGGTTATTATACCGTCAAGGACTGTGTGAC TATTGACGTCCTTCCCCGTACGCCGGGCAATAATGTTTATGTTGGT TTCATGGTTTGGTCTAACTTTACCGCTACTAAATGCCGCGGATTGG TTTCGCTGAATCAGGTTATTAAAGAGATTATTTGTCTCCAGCCACT TAAGTGAGGTGATTTATGTTTGGTGCTATTGCTGGCGGTATTGCTT CTGCTCTTGCTGGTGGCGCCATGTCTAAATTGTTTGGAGGCGGTCG
AGCT The monolayer was formed with 50 mg / ml of triblock copolymer (TBCP 6-33-6, OH-PMOXA- (PEG ligand) -PDMS- (PEG ligand) -PMOXA-OH, Polymer Source Product ID: P3691B - MOXZDMSMOXZ) in oil and nanopores (MS- (G75S / G77S / L88N /
104/106
D90N / D91N / D93N / D118R / Q126R / D134R / E139K) 8) pre-inserted in the chip.
The chip was then inserted into the slide and the solution manually removed by the pipette and reinserted.
Then 1.5 nM DNA (sense filament sequence SEQ ID NO: 39), 500 nM helicase, 10 mM MgCl2 and 1 mM ATP were added to 150 μl of buffer 1. The solution was then pipetted through the chip through the chimney in the lid and let it diffuse to the nanopore.
The data were recorded for 1 hour at +120 mV, with a potential movement to 0 mV and then -50 mV every 5 minutes, to obtain helicase events in the nanopore.
The movement of helicase-controlled DNA to unbound DNA (sense strand sequence SEQ ID NO: 39) through an MS- nanopore (G75S / G77S / L88N / D90N / D91N / D93N / D118R / Q126R / D134R / E139K) 8 inserted into a triblock copolymer (TBCP 6-33-6, OH-PMOXA- (PEG Binder) -PDMS- (PEG Binder) - PMOXA-OH, Polymer Source Product ID: P3691B-MOXZDMSMOXZ) was not detected.
The pore was observed to block under the tested conditions but no helicase-controlled DNA movement was mentioned.
Example 6 This Example describes how helicase-controlled DNA movement was observed for stranded DNA when exposed to an MspA nanopore embedded in a triblock copolymer.
The chip has 128 reservoirs with platinum electrodes and an opening of 30 μm with a common platinum electrode attached to the lid.
The monolayers were formed with a 50 mg / ml solution mixture of triblock copolymer (TBCP 6-33-6, OH-PMOXA- (PEG Linker) -PDMS- (PEG Linker) -PMOXA-OH, Polymer Source Product ID: P3691B-MOXZDMSMOXZ) in oil.
The nanopore (MS- (G75S / G77S / L88N / D90N / D91N / D93N / D118R / Q126R / D134R / E139K) 8) was then added to the chip in the buffer.
The reagents were just added
105/106 through the top of the chip (cis side) once the chip has been formed. The experiment was carried out with 625 mM sodium chloride, mM potassium ferricyanide, 75 mM potassium ferrocyanide, 100 mM HEPES, pH 8.0 (buffer 1). The MspA mutant used was MS- (G75S / G77S / L88N / D90N / D91N / D93N / D118R / Q126R / D134R / E139K) 8. The DNA sequence used in this experiment consists of double-stranded 400mer DNA (SEQ ID NO: 40 shows the sense strand sequence) and a short complementary DNA strand with cholesterol attached to the 3 'end (SEQ ID NO: 41) that can hybridize to a portion of SEQ ID NO: 40. SEQ ID NO: 40 TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTG GTTGTTTCTGTTGGTGCTGATATTGCGCTCCACTAAAGGGCCGATT GACGCTCCACTAAAGGGCCGATTGACCCGGTTGTTTCTGTTGGTGC TGATATTGCTTTTGATGCCGACCCTAAATTTTTTGCCTGTTTGGTTC GCTTTGAGTCTTCTTCGGTTCCGACTACCCTCCCGACTGCCTATGAT GTTTATCCTTTGGATGGTCGCCATGATGGTGGTTATTATACCGTCA AGGACTGTGTGACTATTGACGTCCTTCCCCGTACGCCGGGCAATAA TGTTTATGTTGGTTTCATGGTTTGGTCTAACTTTACCGCTACTAAAT GCCGCGGATTGGTTTCGCTGAATCAGGTTATTAAAGAGATTATTTG TCTCCAGCCACTTAAGTGAGGTGATTTATGTTTGGTGCTATTGCTG GCGGTATTGCTTCTGCTCTTGCTGGTGGCGCCATGTCTAAATTGTTT
GGAGGCGGTCGAGCT SEQ ID NO: 41
AGCGACTAACAAACACAATCTGATGGCTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT / 3 ColTEG / The monolayer was formed with 50 mg / ml of triblock copolymer (TBCP 6-33-6, OH-PMOXA- (PEGA-PEGA-Linker) Source Product ID: P3691B-
106/106
MOXZDMSMOXZ) in oil and nanopores pre-inserted in the chip.
The chip was then inserted into the slide and the solution manually removed by the pipette and reinserted.
Then 1.5 nM of DNA (sense filament sequence of SEQ ID NO: 40 and filament SEQ ID NO: 41), 500 nM helicase, 10 mM MgCl2 and 1 mM ATP was added with a short complementary tie to 150 μl of buffer 1. The solution was then pipetted through the chip through the chimney in the lid and allowed to diffuse into the nanopore.
The data were recorded for 1 hour at +120 mV, with a potential movement to 0 mV and then -50 mV every 5 minutes, to obtain DNA movement controlled by helicase through the nanopore.
The helicase-controlled displacement of stranded DNA (sense strand sequence of SEQ ID NO: 40 and complementary short strand strand of SEQ ID NO: 41) through an MS- (G75S / G77S / L88N / D90N / D91N / D93N / D118R / Q126R / D134R / E139K) 8 inserted in a triblock copolymer (TBCP 6-33-6, OH-PMOXA- (PEG Binder) -PDMS- (PEG Binder) -PMOXA-OH, Polymer Source Product ID: P3691B-MOXZDMSMOXZ) was detected.
Twelve helicase-controlled movements of DNA were detected during the course of a positive 5-minute cycle.
The average time between helicase-controlled DNA movements was 0.5 seconds.
Therefore, by tying the DNA to the triblock copolymer, it is possible to observe the DNA movement controlled by the helicase that was not detected in a similar experiment using untied DNA (example 5).

权利要求:
Claims (15)
[1]
1. Method for determining the presence, absence or characteristics of an analyte, characterized by the fact that it comprises (a) attaching the analyte to a membrane, in which the analyte is not attached to the membrane via a detector present in the membrane and (b) letting the analyte interact with a detector on the membrane and thereby determining the presence, absence or characteristics of the analyte.
[2]
2. Method according to claim 1, characterized in that the membrane is an amphiphilic layer or a solid state layer.
[3]
Method according to claim 1 or 2, characterized in that the analyte is present in a concentration of about 0.001 pM to about 1 nM, such as less than 0.01 pM, less than 0, 1 pM, less than 1 pM, less than 10 pM or less than 100 pM.
[4]
Method according to any one of claims 1 to 3, characterized in that the analyte is attached to the membrane via a polypeptide or a hydrophobic anchor.
[5]
5. Method according to claim 4, characterized by the fact that the hydrophobic anchor is a lipid, fatty acid, sterol, carbon nanotube or amino acid.
[6]
Method according to any one of claims 1 to 5, characterized in that the analyte is attached to the membrane via a linker.
[7]
Method according to any one of claims 1 to 6, characterized in that the detector comprises a transmembrane pore or a transmembrane protein pore.
[8]
8. Method according to claim 7, characterized by the fact that the transmembrane protein pore is derived from Msp or α-hemolysin (α-HL).
[9]
9. Method according to claims 7 or 8,
characterized by the fact that the method comprises: (a) letting the analyte interact with the detector; and (b) measure the current that passes through the pore during the interaction and thereby determine the presence, absence or characteristics of the analyte.
[10]
Method according to any one of claims 1 to 9, characterized in that the method is for (a) identifying the analyte or (b) estimating the sequence of, or sequencing a target polynucleotide.
[11]
11. Method for sequencing an analyte that is a target polynucleotide, characterized by the fact that it comprises: (a) carrying out the method as defined in any one of claims 1 to 10, wherein the detector comprises a transmembrane pore, such that the target polynucleotide moves through the pore; and (b) measuring the current that passes through the pore as the target polynucleotide moves with respect to the pore and thereby determining the sequence of the target polynucleotide.
[12]
12. Method according to claim 11, characterized in that the method comprises: (a) attaching the target polynucleotide to a membrane; (b) letting the target polynucleotide interact with a detector present in the membrane, where the detector comprises a transmembrane pore and a protein that binds polynucleotide, such that the protein controls the movement of the target polynucleotide through the pore and nucleotides in the target polynucleotide to interact with the pore; and (c) measuring the current that passes through the pore as the target polynucleotide moves with respect to the pore and thereby determining the sequence of the target polynucleotide.
[13]
13. Kit for sequencing an analyte that is a target polynucleotide, characterized by the fact that it comprises (a) a transmembrane pore, (b) a protein that binds polynucleotide and (c) means for attaching the target polynucleotide to a membrane.
[14]
14. Apparatus for sequencing an analyte that is a target polynucleotide, characterized by the fact that it comprises (a) a membrane, (b) a plurality of transmembrane pores in the membrane, (c) a plurality of proteins that bind polynucleotide and ( d) a plurality of membrane-bound target polynucleotides.
[15]
Apparatus according to claim 14, characterized by the fact that the analysis apparatus comprises: a sensor device that is capable of supporting the membrane and the plurality of pores and is operable to perform the polynucleotide sequencing using the pores; and at least one reservoir to contain the material to perform the sequencing.

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法律状态:
2020-08-18| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|

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2021-01-19| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

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2021-11-03| B350| Update of information on the portal [chapter 15.35 patent gazette]|

优先权:

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申请号 | 申请日 | 专利标题

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US201161490860P| true| 2011-05-27|2011-05-27|

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US61/490860|2011-05-27|

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